Tests for multimap removeAll(): ensure empty collection returned on removeAll of unmapped key. Ensure collection returned by removeAll is uncoupled from the multimap.
Correct Multimap documentation - unmapped keys return empty collections, not null.
Bump version to 0.10.3
Merge pull request #45 from cbracken/multimap-docs

Corrections to Multimap docs: unmapped keys map to the empty collection (not null).