Add version to outgoing messages

- Added constant for version of release in constants.py
- Added 'v' value representing node's version number in send messages

This version number will help us see what version nodes are running on when diagnosing issues in the future.
Add timeout to resolve row lock bug

Simultaneous access to a row when writing and reading will cause an exception. This allows the proces to wait until it's available and then write instead.
Create only one zmq context to reduce overhead

Creating a zmq context for each PeerConnection object is wrong and creates a massive overhead.

Move context creation to parent class
Remove redundant context creation
Fix executable bit check to work on Mac OS X.

* Ignore results from virtualenv folder.
update brew installer url
Reduce threading in market.py

* These operations end up accessing the DB but pySQLite doesn't
  support multithreaded access.
Do not use string_types from six.

* No reason to fake Python3 compatibility in just one module.
Remove six from requirements.

* Any package that requires it should install it on its own.
Test keyInRange against unicode.

* Fix the naming convention in the other tests.
project status update
Disallow function redefinitions (E0102).
Unshadow function definitions.

* Silence pylint warnings on behave tests. Naming all steps
  as `step_impl` is conventional.
Disallow lost exceptions (W0150).

* Exceptions should be explicitly caught and handled.
Handle exceptions explicitly.
market: reduce coupling between market and DHT implementation.

* Also decrease coupling by removing the return value,
  since it is not used anywhere.
transport: Refactor transport.store

* Turn it into a pure wrapper around dht.iterativeStore
  to reduce maintenance cost for changes in DHT.
Add a rollover count so limits are obeyed

Limits in file size don't seem to obey unless set to > 1.
More sane logging level by default
an up to date changelog with the latest version number is necessary for the debian building tools. re-introducing changelog update lost on release-0.2.0 branch