Filter instance list (and all lists) by string contains

[doublerebel]

Posting re:discussion with @trentm in #102

It would be great to filter triton instance list by =~ as is possible with triton image list. That's the only place I still need json+jq.

[doublerebel]

This may be overkill, but I did just port Riemann's query language to Nodejs. It's designed to filter a key/value structure so it can filter on all these expressions. I'm pretty sure the only thing that would need to change in my parser is the keywords. Then you wouldn't have to maintain your own filter parser.

EDIT: Would be pretty easy for me to factor out the keywords to make that a reusable module.