Fix iPhone PNG color issues when loading images from memory in NanoVG

small typo fix and documentation fix

Allows setting the `NVG_MAX_STATES` number.

Currently, `NVG_MAX_STATES` is set to 32. But it’s not enough sometimes in my case. This commit allows defining the preferred `NVG_MAX_STATES` number.

Fixes memory leaks caused by full font images.

Fixes stbtt implemention

This commit fixes the issue mentioned by 0b37350df7 (r63095702)

Fixes FreeType errors when dealing with multiple NVGcontext objects.

Originally there is only a shared `FT_Library` object. However, if we create multiple `NVGcontext` objects and as soon as we delete one, the shared `FT_Library` object will be released, too. And that would cause a problem for the rest of `NVGcontext` objects.

Update fontstash.h

* change call order in `fonsDeleteInternal` so that free memory isn't passed to `fons__tt_done`

This reverts commit e5f559523f.

This reverts commit 69e1a47511.

Only reverts fontstash.h, not the whole commit.

Continous Integration for nanvog

Does not build examples (yet), due to technical
problems with the older ubuntu version being used
by github.

Fixed text vanishing when the transform is vertically flipped

Single-byte typo fix

fix for freetype glyph loading

Added a preprocessor definition to disable the use of stb_image

Fixed Signed/Unsigned Comparison Warning

In Visual Studio 17, I get warnings related to these variables:
````
fontstash.h(241): warning C4018: '<': signed/unsigned mismatch
fontstash.h(242): warning C4018: '<': signed/unsigned mismatch
````

Making them unsigned fixes it.

Bind a dummy texture in setUniforms when compiling with emscripten

- nvgTextBreakLines: wordMinX was relative to rowStartX, which caused
problems when rowStartX change on line break, but wordMinX was still
relative to the previous rowStartX
- fixed font size on perf graphs
- made demo to use row minx/maxx instead of row->width
- fixed demo hover distance

fixes the WebGL error "RENDER WARNING: there is no texture bound to the unit 0"" in Chrome