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.

Add support for bgfx

This commit updates the `nvgBeginFrame()` function to forward the received `devicePixelRatio` parameter to the `renderViewport()` function so it is possible to configure the environemnt correctly when using `bgfx` backend.

Fixing clang compiler warnings.

Fix typo in nvgCreateFontMem() description

- nvglImageHandle was changes to contain GL postfix, changed GL utils
to use that too
- fixed silly failure check bug in FBO demo

Fixed fontstash.h crashing

Fix for issue #172

fixed type usage

in some situations int and GLsizei is not the same type which leads to conversion warnings

Improve the use of NVGLUframebuffer.

The `NVGLUframebuffer` structure contains a `ctx` member but was actually never used. This commit takes advantage of the `ctx` property so there is no need to keep the reference of the context elsewhere after calling `nvgluCreateFramebuffer()`, or it would add difficulty for maintenance. As a result, the `nvgluDeleteFramebuffer()` function only needs to take one `NVGLUframebuffer` instance as the parameter.