Create contextName helper for context lookup
Use depths array rather than passing array args

Approximately doubles the throughput performance of depthed templates and clears the way for doing recursive path lookups in pathed mode.
Avoid depth construction overhead for non-depthed
Implement recursive field lookup in compat mode

Provides the mustache behavior of recursive lookup without the use of depthed paths.

Note that this does incur a fairly dramatic performance penalty for depthed queries.
Merge pull request #819 from wycats/compat-mode

Implement recursive field lookup