Implemented the copy mechanic and added a summon mechanism

Summoning a minion does not trigger the battlecry or any triggers for
minions being played.
Removed authorship information from files and added a contributors file
Fix for Tracking

Closes #34
Renamed wind_fury to windfury
Migrated hero power tests to their own testing file.
Added a test for hero power being used only once per turn
Additional testing for Gladiator's Longbow
Removed __init__.py files from coverage testing
Changed the way overload is handled
Implemented Unbound Elemental

This commit marks all shaman minions as complete!
Implemented Feral Spirit
Fixed some stuff with .summon()
Implemented Forked Lightning
Implemented Frost Shock
Implemented Hex
Implemented Lava Burst
Fix for Polymorph
Implemented Lightning Bolt
Fix for Hex
Created replace method for minions