Fix UnicodeDecodeError when POST'ing binary files

When Resources/Operations are constructed from api-docs, all fields (e.g. 'method') are unicode. In python 2.7 httplib attempts string concatenation to construct POST bodies, which means that UnicodeDecodeErrors occur if one includes binary data as a parameter. Rather than change all api-doc fields to 'str', this branch casts only fields used in httplib.

v0.7.4

Encode params to utf8.

Log level debug for request logging

v0.7.3

v0.7.2

Allow headers to be sent with api doc request

v0.7.1

Resolves issues arriving from mutation of async client.