Tethne: experimental release v0.4.0-alpha

Changes from v0.3.1-alpha

• Continued development of Flask-based web application.
• --local flag in CLI looks for needed libraries in local directory.
• Documentation rebuild, including new tutorials.
• Added services subpackage with geocode module.
• networks.authors.coauthors method has new geocode option, that uses Google's geocoder to parse institution names.
• Added new network, networks.authors.institutions, based on coauthorship and institutional affiliations.
• Switched to custom TethneGraphMLWriter class (based on NetworkX's GraphMLWriter) that uses attribute names rather than generic IDs for attribute keys (avoids import bug in Gephi).
• Various bugfixes and performance enhancements (e.g. coauthors runs much faster now).