Variable initialization, unused var removal, and casts.

- changed tessellation threshold from 0.3 to 0.25
- fixed scissor AA on retina
- fixed stroke AA on retina

Removed some unused variables to silence compiler warnings, initialized
variables to 0, added varialbe casts to silence additional compiler
warnings.

- merged font stash optional FreeType support

- added support to take screen shots
- added support to render to frame buffer using premultiplied alpha
- fixed spelling NVGaling -> NVGalign

fixed error return value

- added better logic for inner bevels
- tweaks to reduce overdraw at edges
- fixed convex shape logic

reduces warnings

Reset pixel storage settings after load texture.

Improve VC support

Remaining change for VC support

- Renamed FPScounter to PerfGraph
- dump avg times at exit

- moved performance counter and drawing to separate file
- tweaks to performance drawing

Support for cases where the gl header does not include GL_ARB_TIMER_QUERY

Quick guard against NULL ptr dereference of texture type on CPU side

Timing for CPU inner frame and GPU inner frame added

Needs names for the UI components to distinguish them, and probably stacking vertically for easier comparison.

- implemented missing scissor from draw triangles
- buffer a whole frame of uniforms
- moved paint to uniform conversion earlier
- simplified render loops and data structures
- renamed bunch of things
- combined shaders, use define to disable AA

- correct fix for ubo memroy allocation (use returned alignment instead
of struct size)
- separated convex fill to own command type
- moved uboPos to call struct

Added glMapBuffer cast

Cast void* to char* to remove compiler warning in C++ project in VS2013

Fixed some warnings with MS compiler

Moved nanovg_gl3buf.h to uniform buffers