Merge pull request #2 from ReadyTalk/master

Update personal avian to current readytalk/avian
This solves a class cast exception from a call to .values() from an UnmodifiableMap.  It also solves an issue where you can modify an unmodifiable collection through the Iterator or ListIterator (depending on the structure type).
Removed exception message based on Josh's recommendation
Added a simple test to show the original issue
Merge pull request #71 from jentfoo/issue70

Fix ClassCastException in UnmodifiableMap as well as fix modifying unmodifiable structures through iterators