= http: Always encode sub-delims in query names and values.

Per this W3C recommendation:

http://www.w3.org/TR/1999/REC-html401-19991224/appendix/notes.html#h-B.2.2

Servers are permitted to treat an un-percent-encoded semicolon as
a query parameter separator. Not many, but some, servers follow this
recommendation, so ensure that they are encoded in the URIs that
Spray renders avoid misinterpretation.