added test for invalid input
removed syntax sugar getters from card
moved mana cap handling into player
inlined healing
documented and refactored strategies

+ javadocs
+ Strategy converted into abstract class
deduplication of constructors
static import of Action
added game with two players
drawing of initial hands
player switching and mana slot retrieval
mana refill mechanism, renamed maxMana into manaSlots
blank lines--/++
card drawing
added code climate badges
Merge pull request #12 from bkimminich/develop

refactorings & more JS impl