Lots of improvements [see full commit message]

- flatten files for text-mate exporter, everything in snippets
  will be put in root of export dir
- documented yaml-front
- changes snippet consumption pattern
- updated sample snippets
- new TODOs
- watch:dev target to run exporters when stuff changes
- rename AMDSnippets output to SublimeSnippets
- ST3 isntall instructions
- comments and error handling in text-mate-exporter
- error checking and comments in snippet-loader
- make abbreviationPrefix overridable by snippet
- strip newlines from __content cuz where'd it come from tho
- text-mate translator now works correctly