Adds ImmutableIntMap
Makes Engine return an ImmutableIntMap in getEntitiesForFamily()
Makes ImmutableEntries, ImmutableValues and ImmutableKeys extends Iterable
Merge branch 'immutable' of github.com:libgdx/ashley into immutables
Renames iterator types in ImmutableIntMap for simplicity and correctness
Actually forbids calling remove on immutable iterators
Fixes ImmutableIntMap interface
Merge branch 'master' of github.com:libgdx/ashley into immutables