Version 1.61 + todo additions

Fix for atof with glibc.

Added ImAtof, ImCeil, ImFloorStd to IMGUI_DISABLE_MATH_FUNCTIONS for consistency. Configuration comments.

Added IMGUI_DISABLE_MATH_FUNCTIONS in imconfig.h to make it slightly easier to redefine wrappers to std maths functions such as fabsf(), fmodf(), etc. Comments.

Data types: DragScalar, InputScalar: default parameters. Added IM_STATIC_ASSERT(). Comments.

Merge branch 'data_types' ...

# Conflicts:
#	CHANGELOG.txt
#	imgui.cpp

Internals: Made ContentsRegionRect absolute to reduce confusion. Renamed InnerRect to InnerMainRect, renamed WindowRectClipper to OuterRectClipped.

Internals: Nav: Extracted code into a NavClampToVisibleAreaForMoveDir() + fix debug code + inline some functions, removed obsolete EndChild() comment.

Internals: Declaring DragBehavior, SliderBehavior in there (no warantee given) as they may be useful to custom widgets.

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

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

Internals: Removed unnecessary allocation indirection for g.LogClipboard (this only made sense when there was a global context instance)

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)

Internals: A few selected math helpers are now using template to handle all supported types. Added ImPow() to wrap float/double in a standard manner without calling pow(double) when not needed in Drag code.

Internals: Data types: Made format string optional. DragBehavior: Moved a bit of code outside of the template. Slider tidying up. Removed unnecessary call to fabsf().

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)

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