Moved DragScalar, InputScalar, SliderScalar to imgui.h as well as ImGuiDataType (#320, #643, #708, #1011)

Settings: Comments (#923, #993)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/imgui_impl_dx9.cpp
#	imgui.cpp
#	imgui.h

Settings: Added LoadIniSettingsFromDisk(), LoadIniSettingsFromMemory(), SaveIniSettingsToDisk(), SaveIniSettingsToMemory(), io.WantSaveIniSettings. (#923, #993)

Viewports: Comments on ImGuiConfigFlags_DpiEnableScaleViewports and ImGuiConfigFlags_DpiEnableScaleFonts. (#1542)

SliderScalar, VSliderScalar(): Support for any data types. Tested with various ranges/limits. Note that Drag/Slider/Input currently fail if the format string doesn't preview the actual value. Will fix next. (#320, #643, #708, #1011)

Made IMGUI_DISABLE_OBSOLETE_FUNCTIONS exceptionally not affect the layout of ImGuiIO. (#1695)

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)

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)

Comments about using "power curves". Demo tweaks. (#648)

Clarified usage of ListBoxHeader() before we rename those functions + fixed demo code that didn't honor it correctly. (#1783)

DragDrop: Removed const qualifier from ImGuiPayload 's void* data, easing casting on user side.

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)

Renamed all "display_format" arguments to "format" to emphasis that they also affect rounding of values. (#648, #642)

Comments, minor tweaks

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: 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)

Viewport: Moved ScaleWindow* code in a proper location. Various comments.

Added IMGUI_CHECKVERSION() macro to compare version string and data structure sizes in order to catch issues with mismatching compilation unit settings. (#1695, #1769)

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

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

Platform: Added platform_io.Platform_SetWindowFocus, Platform_GetWindowFocus function wrappers (unused yet). Exact specs tbd because our simplified concept of focus doesn't necessary match the more complex OS native concepts. (#1542)

Fix various typos.

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: Clamp windows within monitors + fallback rescue window when it is out of sight (e.g. removed monitor, changed resolution) + Win32: declare primary monitor at the beginning of the list. (#1542)

Viewport: Added ImGuiConfigFlags_ViewportsNoMerge flag (to enforce a platform window for all floating windows) + minor tidying up and addition of non-functional wip code.

Viewport, Platform: Added work area in ImGuiPlatformMonitor. Renamed fields. (#1542)

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)

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