Use === for checking constructor type
Use single braces in git grammar
Refactor parser and grammar handling

Grammars now handle stuff like dependencies and tag delimiters, and
overall it should be a lot simpler and safer to define grammars
now. Baba is also more AMD/CommonJS-friendly, as grammars use
Baba.Grammar() to define the grammar instead of polluting the global
namespace.

Baba must now be imported before any grammars. Grammars don't export any
objects or properties. Current usage in browsers:

var baba = new Baba.Parser('my-grammar')
baba.render('path.to.template')
Update task to uglify all JS files
Remove obsolete demo script
Move source files to src subdirectory