Internals: Missing const, some renaming. Tweak legacy fast path.

Internals: Tidying up internal helpers. Fixed a case ImParseFormatTrimDecorations() can return an off by one (out of bound) pointer if the format string is invalid. Extracted ImParseFormatFindEnd() out of TrimDecorations so we can use it to find the format type and replace the %f in old Int apis.

Internals: Fixed DragInt* default format string. InputScalar(), InputScalarN(), removed InputFloatN(), InputInt(). Note that DragInt2/3/4 will %f format strings will currently be broken. (#320, #643, #708, #1011)

Internal: DragScalar(), InputScalar() now support signed/unsigned, 32/64 bits, float/double data types. (#320, #643, #708, #1011)

Internals: DragFloat: Fixed power handling. Use an temporary accumulator and no absolute values so we will be able to manipulate double as well as 64-bit integers. (#1011, #708, #320)

Internals: DragFloat: Removed DragSpeedScaleFast/DragSpeedScaleSlow since it's not yet usable and Nav version doesn't have an equivalent.

Internals: Data types: Added s64, u64 data types. Added support in InputScalar(). Removed internal.h InputScalarEx() to InputScalar(). Removed cheap-relative-operators support in recently added U32 data path, since this is heading toward being legacy code. + Fixed InputDouble parsing code. (#1011, #320, #708)

DragFloat/SliderFloat internal InputScalar trim leading/trailing spaces emitted from the format string when presenting an edit box to the user. (#648) ...

Follow up to 6881d06

Internals: Renamed IsCharIsSpace() to IsCharIsBlank*() to match standard terminlogy and added ascii/u16 variations.

Internals: Added ImGuiDataType_Uint32 data type which is usable with InputScalarEx().

DragFloat, SliderFloat: Rounding scalar using the provided format string instead of parsed precision. (#648)

DragFloat/SliderFloat internal InputScalar trip trailing decoration off the format string when presenting an edit box to the user. (#648)

DragFloat/SliderFloat internal InputScalar relies on the user supplied format string to format and parse value. (#648) ...

The trailing text after the format will be displayed in the InputText but not affect back parsing. Ideally we can try to strip it later.

InputFloat,InputFloat2,InputFloat3,InputFloat4: Added variations taking a more flexible and consistent optional "const char* format" parameter instead of "int decimal_precision". This allow using custom formats to display values in scientific notation, and is generally more consistent with other API. Obsoleted functions using the optional "int decimal_precision" parameter. (#648)

Viewport: Exposing SetNextWindowViewport(). Used in demo and old/obsolete SetNextWindowPosCenter() (which is an interesting case). Fixed back-end likely crash calling GetFocus() after viewport destruction. Fixed metrics crash.

Viewport, Platform: Refresh monitor list (win32, glfw) + avoid calling GetWindowFocus before platform window creation to not require of backend to null-check things inconsistently. (#1542)

Viewport: Removed unnecessary fields (now that the coordinate system is consistent accross viewports): MouseRefPrevViewport, MouseClickedPosViewportId. (#1542)

Viewport, Platform: Using Platform_GetWindowFocus to provide a much stronger heuristic of platform z-order, in replacement for when the back-end cannot provide io.MouseHoveredViewport. The pressure for it to work well increased with the use of viewports by popups/menus. (#1542)

Misc: tweaks + minor changes merged from master to reduce branch drift. Removed code that ended up unused.

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.cpp
#	imgui.h
#	imgui_internal.h

Misc: Comments and shallow/small changes (merged from viewport branch to minimize branch drift).

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/allegro5_example/imgui_impl_a5.cpp
#	examples/allegro5_example/imgui_impl_a5.h
#	examples/allegro5_example/imgui_impl_allegro5.cpp
#	examples/allegro5_example/imgui_impl_allegro5.h
#	examples/allegro5_example/main.cpp
#	examples/imgui_impl_allegro5.cpp
#	examples/imgui_impl_allegro5.h
#	imgui.cpp
#	imgui_internal.h

Internals: Removed unecessary Pos/PosFloat separation, only reason appears to be mostly pre-1.0. The only piece of code that I expected sub-pixel window position to matter actually already round its delta (wrongly so, will fix later/separately if we want).

Viewport: Tidying up AddUpdateViewport() calls. Moved flags argument. Removed extraneous mid-frame call to FindPlatformMonitorFromRect(). (#1542)

Viewport: Fixed issues with popups drifting in particular when reference mouse position become invalid (e.g. changing app focus while viewported-menu is open). Storing monitor index in viewport at beginning of the frame. (#1542)

Internals: Removed misleading ImRect::FixInverted + fix minor formatting in Readme. ...

Demo: Fixed Overlay: Added a context menu item to enable freely moving the window.

Viewport, Platform: Fixed IME positioning for multi-viewport. Moved API from ImGuiIO to ImGuiPlatformIO. Because it is extremely unlikely to people redefined this API manually the moving-forward-breakage is ok. (#1542) ...

SDL2 ime support under Win32 never worked properly because of SDL interferences.

Viewport: Switched to using unified platform-absolute mouse coordinates, which simplify lots of problems and simplify/reduce tricky conversions, makes ImVec2 less ambiguous. Fixed various viewport/windowing/popups/synchronization bugs. Settings on host-viewport are stored as relative (made settings decently compatible between viewport enable/disabled settings). Merged ImGuiViewport::Pos and ::PlatformPos. Tweaked thumbnails. Better, smaller code. (#1542)

Viewport: WIP for Tooltips, Popups, Menus to create their own viewport. Resizing a window allows it to leave the main viewport. (#1542)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_dx10.cpp
#	examples/imgui_impl_dx11.cpp
#	examples/imgui_impl_dx12.cpp
#	examples/imgui_impl_dx9.cpp
#	examples/opengl2_example/imgui_impl_glfw_gl2.cpp
#	examples/opengl3_example/imgui_impl_glfw_gl3.cpp
#	examples/sdl_opengl2_example/imgui_impl_sdl_gl2.cpp
#	examples/sdl_opengl3_example/imgui_impl_sdl_gl3.cpp
#	examples/vulkan_example/imgui_impl_glfw_vulkan.cpp
#	imgui.cpp
#	imgui_internal.h