Merge uniforms into a single uniform array, reducing number of glUniform calls.

Conflicts:
	src/nanovg_gl.h
Fix for issue #162
Add FBO support for GLES

To support FBO for iOS, the current framebuffer and renderbuffer must be restored after calling nvgluCreateFramebuffer(). The framebuffer should also be restored when calling nvgluBindFramebuffer(NULL) as well.
Merge pull request #166 from olliwang/pow2check

Fix for issue #162
Merge pull request #163 from olliwang/gles_fbo

Add FBO support for GLES
Merge pull request #164 from floooh/pr_uniform_array_2

Merge uniforms into a single uniform array
Added nvgCancelFrame()

This commit implements a new nvgCancelFrame() function for the purpose described in #168.

Currently, if calling nvgBeginFrame(), the nvgEndFrame() function must be called to finish the drawing. However, if knowing the drawing would take too much time and want to give up the drawing. There is no way to cancel it. nvgCancelFrame() gives another choice to end the frame without actually drawing.
Merge pull request #169 from olliwang/cancel

Added nvgCancelFrame()