v3.7.0

v3.7.0, 2017-09-05

A new strategy, contributor documentation and internal fixes.

• New strategy Tranqulizer from Axelrod's second tournament:
  #1126
• Improved use of pass_default_arguments and documentation:
  #1127
  #1128

Here are all the commits for this PR:
v3.7.0...v3.6.0