Allow ranging over ring tokens

Would close #170
Handle more than one iteration

Fix kwargs
Set buffer length at correct location

Added incompatible argument exception
Replacing newline
Stricter check on incompatible get_range() arguments
Add docs for start_token, end_token
Fix requireOPP test decorator
Handle false-y start and finish_token
Tests for get_range by token, minor fixes
Merge branch '211-merge'