Extend Sieste to allow for Key/Value searching

Requires updates in anchor/chevalier-common#7

If a query string is given, use that as the wild-card wrapped value in a wildcard key search.

Otherwise, use the key/value pairing as an exact search as a SourceTag (use-based wildcard string wrapping would be required)

The current getParam call returns space-delimited Text objects, which can be split and zipped to compile key and value pairs. (This allows query strings in the form `?key=abc&value=123&key=def&value=456`)

(Travis may not work til chevalier-common is updated)
What happens in the case where `splitOn " " key` and `splitOn " " value` are different lengths? Might be worth encoding them explicitly as pairs?