Fixes how glext header is included.

This commit fixes the issue caused by #357 that nanovg failed to compile on iOS due to the wrong way of including glext header.

Bug fixes to compile under OS X 12.3

To make the examples link correctly under OS X 12.3, you need to include
<OpenGL/glext.h> in the file.  This commit limits what happens by protecting
the include as follows:

    #ifdef __APPLE__
    #   include <OpenGL/glext.h>
    #endif

Thus, this should have no effect on non-Apple systems.

To get nanovg to link correctly under OS X 12.3, it needs to be linked against
the Carbon libraries.  This was missing in the premake4.lua files.  Now fixed.

Improve nvgGlobalCompositeOperation with state

Add image flag to support GL_NEAREST rendering

suppresses all warnings reported by latest Xcode/AppleClang

Better support for CJK characters.

Previously, the Unicode range of the CJK chractaters only includes Chinese charactaters, Japanese Kanji, and CJK Symbols and Punctuation. The range are used by traditioanl Korean as well. This commit further includes Hiragana and Katakana in Japanese, and Hangul Syllables and Hangul Jamo in Korean to make CJK support more complete.

Fixes the bug that text may not render correctly.

This commit fixes the bug that text may not render correctly when glyph is not found in fallback fonts.

Improves to display CJK characters with English words.

This commit improves to display CJK characters mixed with English words so there is less spaces at line breaks.

Fixes line breaks for CJK characters.

handle file IO error

This commit fixes weird line breaks when rendering CJK (Chinese, Japanese, Korean) characters. Each CJK character is more like a word instead of a letter. This commit fixes the logic of line breaks by introducing a new `NVG_CJK_CHAR` code point type and takes special care for formatting text including CJK characters.

nvgRoundedRectEx for varying corner radii

Conflicts:
	src/nanovg.h

Fixes a bug when applying `NVG_IMAGE_FLIPY`.

This commit fixes issue #167 that `nvgImagePattern()` does not handle coordinate well if the specified image applies the `NVG_IMAGE_FLIPY` parameter.

Rename nvglImageFromHandleGL2 -> nvglImageHandleGL2

There was no nvglImageFromHandleGL2 implementation, it must have been
an error during some refactoring

Fallbacks to default composite operation when invalid one is specified.

This commit fixes #300 and #306 that “control may reach end of non-void function” error occurs in `glnvg_convertBlendFuncFactor()`. The function now returns `GL_INVALID_ENUM` for invalid blend factor and if that happens, `glnvg__blendCompositeOperation()` uses default source-over composite operation.

Fixes the kerning value for freetype.

This commit fixes issue #302 that the kerning value returned by freetype is not converted to integer properly.

Support fallback fonts (code refactoring for #299)

This commit fixes the formats as suggested in #299 and fixes stack overflow when using `freetype` backend.

Implements composite operation for blending renderings.

This commit updates the implmentation of global composite operation to follow the advices described at c4b865796d (r74248556)

This commit implements the `nvgGlobalCompositeOperation()` function to support blending between frames. All operations defined in HTML5 canvas API are supported. Also, it is possible to create custom composite operation by calling `nvgBlendFunc()` or `nvgBlendFuncSeparate()` functions.