corpkit: Speed, efficiency and factored

• Speed increases, especially for feature counting
• Multiprocessing for parsing, very useful when you have access to a big machine
• Improved searching for CoreNLP (looking in all paths), automating download and installation
• Simpler backend implementation of keywords and ngrams
• Better documentation, especially at ReadTheDocs
• Code has been refactored and made largely PEP8 compliant, aiding collaboration
• Can now sort by subcorpus name in interrogation.edit() method

Very little difference to the API, however!