use explicit type for mock body

see bblimke/webmock#427
replace webmock stubs with faraday stubs

to correctly handle the serialized JSON
Merge pull request #79 from koenpunt/fix-webmock-invalid-body

use explicit type for mock body
change default content-type to application/hal+json

add application/hal+json to 'Accept' header
add custom middleware for json+hal
Merge pull request #81 from koenpunt/accept-json-hal

Use application/hal+json as default Content-Type and add to Accept header
add faraday connection options without breaking api
merge headers into connection_options
renamed connection_options to faraday_options
default is implicit, non default explicit