Have plugin identify as a command to cut down on unintended parsing

From time to time helga will see a message that starts with '>' and will get a little noisy with haskell errors. I'm sending this PR as a proposal that replaces the use of @match with @command so haskell interpreting happens by request instead of automatically.

Old usage `> "foo"`.

New usage `!h > "foo"` or `!haskell > "foo"`