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.
Merge pull request #667 from hoffmabc/master

[CRITICAL] Add version to outgoing messages
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.
Merge pull request #672 from Renelvon/mac_checkstyle

Fix executable bit check to work on Mac OS X.
Merge pull request #670 from hoffmabc/master

Bug Fixes (single zmq context, timeout in database connection)
update brew installer url
Reduce threading in market.py

* These operations end up accessing the DB but pySQLite doesn't
  support multithreaded access.
Merge pull request #708 from Renelvon/less_threading

Reduce threading in market.py
Remove unused third-party-tools folder.
Merge pull request #710 from Renelvon/no_3rd_party

Remove unused third-party-tools folder.
Factor GUIDMixin definition in a new file.

* Abstract initialization of GUIDMixin inside
  initialization of CryptoPeerConnection
* Coerce string to GUIDMixin when adding contact.
Support unicode GUIDs.

* Add a deprecation comment for future comparisons
  against subclasses of basestring.
Test GUIDMixin.

* Also test CryptoPeerConnection subclassing.
Update documentation.
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.
Merge pull request #693 from Renelvon/guid_is_unicode

Abstract GUIDs. Properly support unicode GUIDs.