Major TODOS:
* clean up a bunch of code duplication in the compiler
* reorganize the compiler
* add support for debug symbols which would make it possible
to provide information about what part of the source caused
a runtime error.
* {{}} escape their contents, {{{}}} and {{& }} do not
* Add support in the parser, tokenizer and AST for partials
with context (support is still not there in the runtime)
* Fix some inconsistencies with the old behavior involving
the correct printing of null and undefined
* Add Handlebars.Exception
* Fixed an issue involving ./foo and this/foo
* Fleshed out helperMissing in the specs (this will be
moved out into handlebars proper once registerHelper
and registerPartial are added)