Define an initial grammar supporting cmds and piped cmds
Support nested backticked sub-expressions
Test yetibot.parser and note limitations on nested sub-expressions
Move loading/reloading into yetibot.loader namespace
Move command handling into yetibot.handler namespace
Return command result to API
Kill unnecessary parse-event macro
Clean up printlns and docstrings
Support nested sub-expressions with standard POSIX $(...) syntax
Refactor handler to use new parse tree
Support parens inside expressions and use transform options to evaluate the parse tree
Add rest command and trim items in list command
Merge branch 'feature/instaparse'

Fix #214