Merge pull request #9 from jmcotelo/develop

Merging all changes from closed Milestone M1
Now this module uses LibYaml as PyYaml backend if available
added a module for parsing status dump files
Refined the package import. Added a default strategy for the load_n() function, in case of no extraction functor is provided.
Added a graph module for building, analyzing and dumping graphs using ad-hoc data. Fixed some date "typos"
Added code for including the status update termset in the extraction process
Updating changes related to #5: Selected networkx as graph_backend. First draft with dummy functions for some parts of the graph building process.
Parsing status now give the hashtags and mentions in a proper format. Tentative graph building process done for #5.
Minor package changes. Added tag - tag directional edges to the graph building process
More changes for #4 & #5.
 - Added Networkx as preferred backend. (leading to #4 closing).
 - Added a GraphAnalyzer class that will hold all the graph computation needs.
Merge pull request #10 from jmcotelo/M2

Progressing M2 - Closing #4