Update dependency information in README

Change-Id: I73358b3df758f3f23cd4f2d92481c561b0e3e45b
Add example of 'item' API

Change-Id: I5a7062b636a007b55d374e44f163205faa007ef6
PYCBC-196: Convenience methods for Item API

This adds some additional convenience methods and documentation for the
Item API.

Change-Id: I70835ab514f4097d737d52719bf7bab1ec6baad4
Change setUpClass/tearDownClass

Apparently py.test only recognizes these purely camelCase names, rather
than setupClass/teardownClass

Change-Id: Ia520e318f8ccf7f66c25604d92a1a0486d3ef835
Enabled maximum test coverage

Previously, one had to choose between either running the tests against a
real server, or running them against the mock. This was unfortunate as
there were some tests which only functioned on the mock and not on the
real servers, and vice versa

This change allows tests to be executed against the "best" option by
providing several new test classes:

ConnectionTestCase: Generic connection. Either mock or real server
MockTestCase: Only use mock for these tests
RealServerTestCase: Only test against real servers

Reflecting these configuration options, the configuration file may
enable either the mock or the real server or both.

Change-Id: I99deb5b0e04c99faf7c710e763d8a2d4ba41517b
Twisted support

This adds twisted support using the following:

* New private 'async' module which returns future-like objects rather than
  waiting

* IOPS implementation for a twisted reactor

* txcouchbase package supplying a connection wrapping the internal Async
  object

Test enhancements were needed to make sure the test architecture was
usable with Twisted's trial.

Change-Id: I58a94944f6fbf308b307db532bd01d6cf6b9fc05