* Switch to using memory management class from Cython, where I've broken the memory manager out to its own package.
* Add count method to sparsehash wrapper
* Switch feature extractor to use cymem class, rather than deprecated redshift.memory
* Add size reporting for lexicon, and fix memory Pool
* Add from_untagged classmethod to Input
* Fix memory leak caused by misunderstanding dense_hash_map API. Calls to operator[] actually insert the element when not found, which isnt what I wanted. Now use count() to check for membership first.