add ability to set a wrapping interval for world coordinates in the vertex shader
these are used for procedural textures, and with absolute mercator meters across the globe,
we run out of floating point precision starting with slight artifacts at zoom 17, escalating
to significant pixelation and quantization at zoom 19-20
world coord wrapping can be disabled, and there's also a helper function to convert wrapped
coords back to absolute ones (which will reintroduce the precision loss but is fine for some uses)
count # of frames rendered
demo: add button to take a 'screenshot' of the canvas and save to file
Merge branch 'master' into envmap

Conflicts:
	dist/vector-map-worker.min.js
	dist/vector-map.debug.js
	dist/vector-map.min.js
	src/gl/gl_shaders.js
	src/gl/shaders/polygon_fragment.glsl