- support for stylesheet-defined render modes
- includes injecting GLSL shader snippets into the mode's 'base' shaders
- several other small optimizations (track active modes, lazy mode init on render, avoid calculating some values multiple times in render loop, etc.)
- WIP! pieces of index.html demo are broken (effects switcher, needs to be migrated to mode paradigm)
experimenting with YAML for the style file (for the multi-line string support, for shader snippets)
add procedural dots texture, via @meetar
stylesheet uniforms should be under 'shaders' block
shader snippets can be specified inline, or as URLs (default is now inline)
re-org some demo styles
added procedural wood shader
- add support for style 'macros' (white-listed style computing functions) in YAML styles
- make YAML style support co-exist w/JSON support
- make YAML support optional by moving to separate browserified file (parser is large, not sure we want it in core lib)
- generalize support for code that only needs to run in the main thread (not in workers)
add extracted YAML parser to makefile dependencies
continue to fix/refine YAML stylesheet
add support for stylesheet shader snippets to be inline block of GLSL, or a URL to retrieve GLSL block from
Merge branch 'modes' into yaml

Conflicts:
	dist/vector-map-worker.min.js
	dist/vector-map.debug.js
	dist/vector-map.min.js
move screen spotlight effect to shader snippet
ignore annoying OS X files
Merge branch 'modes' of https://github.com/meetar/tangram into modes
add wood shader to yaml style
explode -> breathe
separate lighting calc from color
allows lighting to be optionally applied or changed in stylesheet shader transforms
other shader cleanup
simplify some checks by doing upfront style post-processing
reset timer when changing modes (just makes demos a little nicer looking)
integrate render modes into demo, refine demo stylesheet
move some lib files to a demos/lib dir, as they are not actually core library depdencies