expelliarmus

• Removed Python 3.4, 3.5, 3.6 support. Apologies to users; found that migrating to Python 3 introduced more issues than expected and so will be removed until development progresses further.
• GCTX files only: added chunking (for data matrix only) and gzip compression (for metadata only). Defaults for this behavior are set for compatibility with cmapM and cmapR packages.
• Issues with travis fixed
• Bug fixes
• Documentation updates