Merge pull request #71 from starwing/master

add support for MinGW.
Fix for issue #72

- scale and letterspacing were mixed in call to getQuad
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.
Merge pull request #74 from elmindreda/master

Replaced hardcoded GLFW link flags with pkgconfig
Include GLFW_INCLUDE_GLCOREARB only on Macs
Improved nvgTextGlyphPositions()

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