Add on_cmd and on_missing_cmd hooks.

on_cmd is a generic handler for all called no matter what.

on_missing_cmd is called for missing commands.
Fix the previous commit
Move generic hook logic into exec_hooks

Now hook_func returns hooks specific to that line, or nothing.
Don't turn None's into strings
Add generic command support to the pretty printer

Fixes #7
Merge branch 'master' of github.com:Elizacat/PyIRC2 into prettyprint-all
Rename hook_func to hook_func_in

This is to prepare for hook_func_out.
Unify hook code for in/out.
Add outgoing pretty printer
Fix minor bug
Fix up the pretty printer
Make super calls last.

This ensures that out events come before in (hopefully!)
Misc fixes
Put prettyprinter last in the hierarchy
Merge branch 'prettyprint-wip'