GL3: Combined vert shaders, fixed half pixel offset
GL3 uber shader

- added milliseconds to fps counter
- smooth fps reading a bit more
- changed GL3 to uber shader
Apply font scaling to nvgTextBounds and nvgVertMetrics
Added OpenGL ES 2.0 back end
Merged GL2 and GLES2 backends

- merged GL ES2 and GL2 backends
- GL2 uses now same structure as GL3
Added MSAA option for backends

- added option to turn off AA fringe generation
- added examples which use no AA fringes and  MSAA
Fixes for GLES2
GLES3