Support hmac with Faraday 0.9.0 forward
Faraday now normalizes request parameters via sorting by default but also
allows
the params encoder to be configured by client.  It includes
Faraday::NestedParamsEncoder
and Faraday::FlatParamsEncoder, but a 3rd party one can be provided.

Sigh. When computing the hmac, we need to normalize/sort the exact same way.

Find out which one is in use or select default, then use that for signing
string
use URI.unescape to unescape signing_string params
correctly check set param encoder
include conditional support for both faraday 0.8.9 and 0.9.0
remove debug message
Merge pull request #11 from joshco/feature/hmac_faraday_090

Support hmac with Faraday 0.9.0 forward