Tor-async-couchdb

Added
- SIGINT handler to all samples which is helpful for scripting tests

Changed
- tornado 4.4 -> 4.5.1

Removed
- ...

Changed
- fixed silly install bug introduced in 0.50.0

Changed
- refine & simplify samples given the samples form the primary project documenation
- python-dateutil 2.4.2 -> 2.6.0
- tornado 4.4.1 -> 4.4
- locustio 0.7.3 -> 0.7.5
- python-keyczar 0.715 -> 0.716
- mock 1.3.0 -> 2.0.0
- flake8 2.5.1 -> 2.5.3

Changed
- removed constraint on pycurl rev; pycurl now needs to be >= 7.19.5.1
- fixed exp_backoff sample
- allow a document ID to be specified when a document is first written
to CouchDB; also added AsyncModelRetrieverByDocumentID which allows
retrieval of a document by document ID; these capabilities are the
recommended pattern for using tor-async-couchdb but there are scenarios
where it is useful

Changed
- requests added to setup.py so DB installer just works

Added
- /_health sample using AsyncCouchDBHealthCheck
- AsyncDatabaseMetricsRetriever async action to retrieve database metrics
- /_metrics sample using new AsyncDatabaseMetricsRetriever

Changed
- ton of async_model_actions.py refactoring
- material improvement in samples
- added AsyncCouchDBHealthCheck integration tests
- all samples now use tornado.curl_httpclient.CurlAsyncHTTPClient - see
[this](http://tornado.readthedocs.org/en/latest/httpclient.html) for a quick
explaination of why curl_httpclient is used instead of simple_httpclient
- if available, detailed timing info describing phases of the interaction
with CouchDB now generates an info level log - see
[this](http://tornado.readthedocs.org/en/latest/httpclient.htmlresponse-objects)
Tornado info and [this](http://curl.haxx.se/libcurl/c/curl_easy_getinfo.htmlTIMES)
libcurl info for a description of the timing details. the log message will look
something like:


2015-08-20T11:52:46.335+00:00 INFO async_model_actions CouchDB took 17.26 ms
to respond with 200 to 'GET' against >>>http://127.0.0.1:5984/tor_async_couchdb_sample/_design/fruit_by_fruit_id/_view/fruit_by_fruit_id?key=%222c794f79e43f4c2093d0fb7057ef978e%22&include_docs=true<<< -
timing detail: q=12.06 ms n=0.01 ms c=0.02 ms p=0.04 ms s=16.81 ms t=16.96 ms r=0.00 ms