Add watch_expr and unwatch_expr
Actually support formats
Add support for a short watch syntax
Get the watch functions out of the way

This way they don't collide with the parser hack and you can still poke
at them
Show the expression itself as a label
Fix the signal for the locals being patched
Support "watch as h <expression>" syntax for formats
Show expression IDs
Support unwatching by ID
Burn watch_var with fire
Bail on bad expressions
Fix crashes in expressions that become broken
Use new style exception matching