Fixed bug in fonsTextIterNext()
Adjusted tessellation

- changed tessellation flatness test which produces less vertices
(especially when using straight lines)
- added nvgDebugDumpPathCache which allows to dump path cache state to
stout
Removed unused function
Added text break line and glyph position functions

- added debug configs for the lib
- added more data for font stash text iterator (ptr to current and next
position in string, code point)
- renamed nvgVertMetrics() to nvgTextMetrics()
- added nvgTextGlyphPositions() which returns glyph x position for the
text
- added nvgTextBreakLines breaks a text into multiple rows based on
newlines and max row width
- tweaked tessellation tolerance
Added multi-line text drawing

- fixed some warnings
- changed nvgLetterSpacing() to nvgTextLetterSpacing()
- added nvgTextBox()
- added nvgTextLineHeight()
- added some documentation
Added some TODOs, no return value for textbox
Fixed text related calculations for hi-dpi rendering

- calculate all text related stuff using scaling
- removed a couple of compiler warnings
- tweaked caret picking
GL3buf backend supports GL2 too (not yet enabled)

- added support for GL(ES)2 for nanovg_gl3buf (something is still not
quite there)
- nanovg now sets all required GL state
- removed compiler warnings about unused vars
Clear frag uniforms before filling