Documentation tweaks, comments

Merge branch 'data_types' ...

# Conflicts:
#	CHANGELOG.txt
#	imgui.cpp

Scrolling: Fixed a case where using SetScrollHere(1.0f) at the bottom of a window on the same frame the window height has been growing would have the scroll clamped using the previous height. (#1804)

TODO list update + Changelog and comments for #1803.

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

Fix to allow compiling in unity builds where stb_rectpack/stb_truetype may be already included in the same compilation unit.

Settings: Comments (#923, #993)

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

Skip missing font glyphs to 1) avoid using space for missing glyphs and 2) allow merging fonts with overlapping ranges. Demo: Fixed displaying ? instead of greyed out empty box. (#1671, #1703)

Ran a spell checker for sanity.

Examples: DirectX9: Comments, updated changelog, notes about usage of imconfig.h (#1790, #1687)

DragInt: Patch old format strings to replace %f by %d when using the DragInt() entry point. (#320, #643, #708, #1011)

Ran a spell checker for sanity.

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)

Nav: Fixed hovering a Selectable() with the mouse so that it update the navigation cursor. Fixed c8b9b2c6 which was incorrect (#787)

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)

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)

SliderFloat, DragFloat: Fix to allow input of scientific notation when Ctrl+Clicking a slider or drag, matching the change done in c19b2781 for InputFloat(). (#648, #1011)

DragFloat, DragInt: Cancel mouse tweak when current value is initially past the min/max boundaries and mouse is pushing in the same direction (keyboard/gamepad version already did this).

InputText: Fixed returning true when edition is cancelled with Esc and the current buffer matches the initial value.

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

Fix various typos.

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

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

Window: Relaxed the internal stack size checker to allow Push/Begin/Pop/.../End patterns to be used with PushStyleColor, PushStyleVar, PushFont without causing a false positive assert. (#1767)

InputText: On Mac OS X, support Cmd+Shift+Z for Redo. Cmd+Y is also supported as major apps seems to default to support both. (#1765)

Columns: Fixed a bug introduced in 1.51 where columns would affect the contents size of their container, often creating feedback loops when ImGuiWindowFlags_AlwaysAutoResize was used. (#1760)