Implement GET /{db}/{docid}/{attname} API call
Support request with Range header against attachments
Fix documents test case name (ouch...)
Ensure that assert_request_called_with checks all the actual params

Fixes Document.exists and Attachment.exists methods call with no rev.
Don't encode .read-able objects to JSON
Implement PUT /{db}/{docid}/{attname} API call
Implement DELETE /{db}/{docid}/{attname} API call
Fix docstings markup
Require aiohttp 0.9.1
Use HttpStreamResponse for retrieving attachments
Workaround aiohttp request with filelike objects

KeepSafe/aiohttp#153
Fix AttachmentReader.read method

aiohttp.StreamReader uses -1 instead of None for reading all the data.