Added type-safe IAnonymousTagContainer.getTags() method

This method checks if all entries are of the given type, and returns them
as a List<T>, where T is the tag class. This makes it easier to iterate
over items of equal types.
Added type-safe INamedTagContainer.getTag() method

This method checks if the tag exists and if the type matches the expected
one. This makes it easier navigating in compound tags.
Added methods to TagCompound to directly access values
ReadWriteTest verifies read tag with new read API
Added javadoc for new read methods
Merge pull request #3 from Yogu/typesafe-api

Simpler read api