Added beginnings of logic for berserk attacks
- Added unit tests for BMAttackSpeed
- Added logic to halve the size of a berserk die after performing a berserk attack
Merge branch 'speed' into berserk
Added partial logic to change the berserk die after performing a berserk attack.

Missing is the list of skills that are lost after performing a berserk attack.
- Added unit tests to test Berserk attacks in a game context
- Generalised attack checking code to use BMSkill::attack_types()
Changed many function calls to call by reference, to allow change of die type from swing die to normal die after performing a berserk attack
Fixed swing die replacement during berserk attack to keep the original owner information
Made database and BMInterface changes to load_game() and save_game() so that chosen swing values persist even when the swing dice themselves do not exist any more
- Added unit tests to check that the swing values are cleared from the database at the end of the game
- Added a unit test to check that berserk dice cannot perform skill attacks. ***CURRENTLY FAILING***
Added logic to stop berserk dice from participating in skill attacks
Added test cases to BMAttackBerserkTest.php
Merge pull request #123 from blackshadowshade/berserk

Added berserk attacks