This commit updates font stash to render glyph's bitmap data on demand. This change is intended to fix the issue that `nvgTextBounds()` may return an unreliable result when font atlas is full. This situation usually happens when auto scaling a large font text to fit a small rectangle.

The `fons__getGlyph()` function now accepts a new parameter indicating whether bitmap data is optional, and only `nvgText()` requires it. All of `nvgTextGlyphPositions()`, `nvgTextBreakLines()`, `nvgTextBounds()` and `nvgTextBoxBounds()` functions are changed to work without glyph’s bitmap data.

for nvgluCreateFramebuffer

Fixed return value of nvgText to be the position after the rendered
string, also fixed scaling of the value.

This commit adds a new `nvgShapeAntiAlias()` function for turning on/off antialias for specific shapes.

This commit fixes the bug that `glnvg__renderFill()` allocates unused quad vertices for `GLNVG_CONVEXFILL`, which causes unused vertices uploaded to the GPU.

Besides, the quad for the `GLNVG_FILL` type is changed to drawn by `GL_TRIANGLE_STRIP` instead of `GL_TRIANGLES` so two more vertices can be reduced per quad.

In one of my test case, I need to paste an image to a framebuffer about 5,000 times, and this change would reduce the total number of uploaded vertices from `52,106` to `22,476`. It is good for FPS and battery consumption.

This commit moves the `discard` instruction in the fragment shader to an earlier position to avoid performing calculations whose results are unused.

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

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.

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.

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

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

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.

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

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

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.

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

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

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.

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.

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

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

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.