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

- use regular uniforms for once-per-frame values
- set tex sampler when using NANOVG_GL_USE_UNIFORMBUFFER

- fixed copy/paste bug in bevel calculations

- line caps did not consider AA width

Made FreeType support a bit clearer

Removed GL_BLEND disable and enable inside glnvg__fill() to prevent performance warning.

"Fragment Shader is going to be recompiled because the shader key based on GL state mismatches."

Make sure fons__tmpalloc returns a 16-byte aligned pointer

- use one not used macro for all

- changed remainder of allocations to follow same 1.5x patters
- do not leak memory when realloc() fails
- added error handling in case allocations fail

- increased initial buffer sizes
- change all allocator patterns to over allocate by 1.5x
- fixes bug where nvgl back-end was not allocating +n as requested

Set glFrontFace in glnvg__renderFlush

Removed GLFW 2 option macro

GLFW_NO_GLU is a GLFW 2 feature.  GLFW 3 does not include the GLU header
by default.

- added glyph min/max x
- fixed first glyph position

Replaced hardcoded GLFW link flags with pkgconfig

The GLFW library path and link flags may differ between Linux
distributions.  This makes the build system use the GLFW pkgconfig file,
which hides such differences.

- scale and letterspacing were mixed in call to getQuad

add support for MinGW.

fixes texture formats for GLES2/GLES3

- make default uniform struct align 4

- added nvgCurrentTransform() which allows to get the current
transformation matrix
- added skew x/y transforms
- exposed functions 2x3 matrix functions
- exposed point transform
- added deg/rad conversion functions

- added documentation about changed GL state
- made old GL2 and GL3 backends obsolete

- added test for multiple stroke widths
- allow stroke width down to 1px size, then scale with alpha
- fixed textBoxBounds() in hi-dpi

- nvgTextBounds() API changed, assumes x,y as input too
- fixed nvgTextBounds() return values
- added nvgTextBoxBounds()
- text line width is handle more consistently
- added note about return values of text measure funds
- changed demo to show text(box)bounds usage

- made uniform buffer support behind separate define for easier toggling
- calculate scissor and stroke alpha outside type selection to simplify
the shader (or else it produces rendering artefacts)
- restore default pixel store settings instead of restoring old state
- set active texture to 0 when starting to render a frame

- 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

- calculate all text related stuff using scaling
- removed a couple of compiler warnings
- tweaked caret picking

- fixed some warnings
- changed nvgLetterSpacing() to nvgTextLetterSpacing()
- added nvgTextBox()
- added nvgTextLineHeight()
- added some documentation