Fix typo
Don't use any limits for feeds buffer by default

Let users set own one depending on their needs.
Get rid all maybe_set_param
Rename all *.remove methods to *.delete

"Delete" word is correct one when we speak about electronic information.
Also it clearly associated with the related HTTP method which would be
performed.
Support checks for config options existance
Use "yield from" in tests
Use context manager to define mocked responses
Limit test function execution by 5 seconds
Add testing targets

By default all the tests runs against mocked aiohttp.request. However,
we also need to run test suite against real CouchDB instances to verify
that our code is really works. The target thing will control this moment
defining whenever is need to proxy a call to real aiohttp.request
function and when to use a fake response from it.
Add helpers to run functional testing
Run client tests always against mocked aiohttp.request
Adopt server tests to run against CouchDB instance
Adopt database tests to run against CouchDB instance
Fix setting names for database security
Move database security tests into own case
Adopt document tests to run against CouchDB instance
Adopt attachment tests to run against CouchDB instance
Fix request with Accept-Ranges header
Workaround aiohttp issue about decompressing empty payload
Fix copy-pasted tests