Clean up global commands

TrailerTrash registers a few global commands, they have all been updated
to be prefixed with `Trailer`

- `Trim` -> `TrailerTrim`
- `Trailer` -> `TrailerToggle`
- Added `TrailerShow`
- Added `TrailerHide`

Switch to use `2match` instead of `match`, per the [vimdoc recommendation](http://vimdoc.sourceforge.net/htmldoc/pattern.html#match-highlight).

Also refactored the blacklist and match logic.