Some corpus testing

Corpus loading isn't fully covered by tests yet
Merge remote-tracking branch 'origin/master' into corpus-testing

Conflicts:
	corpustools/corpus/tests/classes.py
Small fixes for import errors
Much moar testing
IO testing
Small updates to get tests to pass largely
Merge pull request #155 from kchall/corpus-testing

Corpus testing - io covered (except for output methods), classes mostly covered except for segment, feature and environment classes