start updating for faraday v0.9.

RackCompatible middleware will never work :(
respect HTTP spec for 301 redirects in standards mode

Previously 301 was always converted to GET, even with
`:standards_compliant => true`. Now when opted into standards mode, 301
will remain unchanged, as per HTTP/1.1 spec.

http://pretty-rfc.herokuapp.com/RFC2616#status.301

Fixes #66
convert caching middleware tests to rspec
add spec for :ignore_params option of caching middleware
Fix typo in RFC number
Update build matrix
Fix tests on Rubinius
Update .gitignore to the .idea/ folder created by RubyMine IDE
Actually fix tests on Rubinius

The rubysl-json gem has been yanked so use the json gem instead.
Update Travis settings for Rubinius

/cc @brixen
Add a Gzip middleware
fixup private
Refactor gzip middleware to reduce ABC complexity
Enable cane quality checks on Ruby 2.0+ as well
Updated middleware registry for faraday 0.9
Missed comma