- set stb_image flags so that it loads correct data in iPhone

update upstream stb things.

Auto detect and resize text altas texture.

allows for nanovg_gl prototypes to be declared simultaneously

Tweaked premake to remove some windows warnings.

second attempt at avoiding warnings at /W4 on vs2013

use -1 as the 'no scissor' value, rather than 0, so that 0 width still scissors

Memory leak + small fixes

fix nvgCreateImageFromHandle for GLES2/3.

- fixed stroke cap tessellation amount calculation

- added nvgQuadTo, draws quadratic bezier curve segment

- all colors in the shader is handled as premultiplied
- removed alphaBlend param from nvgBeginFrame(), it became obsolete
- added NVGL_TEXTURE_PREMULTIPLIED flag
- separated FBO example
- FBOs are treated as premultipied for correct alpha
- changed FBO storage from depth/stencil 24/8 to stencil 8
- moved discard to end of shader which restores the render speed again

- added (optional) 3-pass stencil trick to stroke rendering, reduces
overdraw artifacts, a little slower
- fixed some text bounds issues

- Added alpha for images
- Added global alpha

- fixed glyph position bounds for whitespace

- fixed flags setup in nvglCreateImageFromHandle
- changed frame buffer to only compile on GL3
- changed nvgluCreateFramebuffer() to return FBO struct instead of
filling existing one (for consistency)

add external APIs to GL backend to get native Texture Id.

Relax stroke width limit

Use highp precision when available for GLES

- bezier tessellation was using second control point instead of last
point in error calculation

Explicit cast to make C++ compilers happy

- fixed basic shape windings
- clamp radius of rounded rect so that it behaves nicely when squashed