Minor comments + renaming internal fields

Improved ColorPicker hue wheel color interpolation

Begin(): fixed calling Begin() more than once per frame setting `window_just_activated_by_user` which in turn would set Appearing to true for that frame.

Begin(): renamed locals.

Begin(): Removed unnecessary code (at the time of 1.18 commit e9e0e36, CursorPos was used to compute SizeContentsFit and this was necessary)

Begin(): Tidying up some code, should be a no-op.

TODO, minor tweak

Combo: Internally split into BeginCombo(), EndCombo(), toward a more flexible combo api.

Combo: Removed unnecessary ClearActiveId() call (from era where active combo stored an id, now we just use popup functionality)

Added IsWindowAppearing().

Fixed C4267 conversion from size_t to int.

Demo: Minor coding style tweaks so bgfx copy needs less patching.

InputText: Merged bits from Navigation branch (inc. g.ActiveIdIsJustActivated is only set on the toggle).

Merged from Navigation branch (DragBehavior)

Merge from Navigation branch: 6aa8019

Merged from Navigation branch. TAB/Alt-TAB processing now deactivate if holding Ctrl.

Merged from Navigation branch (misc)

Merged from Navigation branch

Merged from Navigation branch: ...

f71cdd1  Internal tidying up, moved code to CalcNextScrollFromScrollTargetAndClamp() so it can be reused by upcoming nav code.
c816e6c Fixed SetScrollX() handling of center ratio (which actually wasn't exposed publicly). (#323, #246)

Merged from Navigation branch: https://github.com/ocornut/imgui/commit/5cac4926c82a41253bd3540ce1bb4f50b0cfc146 fix title bar color of window under a modal window.

Added GetKeyPressedAmount() (from Nav branch) to be able to measure fast repeat rate accurately. Added internal CalcTypematicPressedRepeatAmount() function.

Merge various minor things (supposedly harmless) from Navigation branch into Master to reduce differences. Some code in NewFrame() has been moved around. (#787)

Merge various minor things (supposedly harmless) from Navigation branch into Master to reduce differences. (#787)

ProgressBar() fixed rendering when straddling rounded area. (#1296)

ImSwap() helper.

Internals: Renamed some ImGuiCorner enums.

ParseFormatPrecision() returns -1 for scientific noation 'e'/'E', RoundScalar() doesn't alter those.

Updated copyright date for 2017, updated Gallery link

Internals: Split some code out of NewFrame() into an Initialize() function.

Added IsMousePosValid() helper.