Add get_timespan() function.
Added get_timespan() function.
Added priority and severity to bugzilla Backend.
Fix issue #28,
Warning message raised when type_analysis is not registered
'Tag' type of analysis added
Merge branch 'master' of https://github.com/VizGrimoire/GrimoireLib

Fix Conflicts in:
	vizgrimoire/filter.py
	vizgrimoire/report.py
Fix syntax error
Added new constructor to Metric so a db connection and filter could be passed.
Merge branch 'master' of https://github.com/VizGrimoire/GrimoireLib
Add new class authors scm metric
Create new classes to control query builder and basic metric class
Add commits class as example
Remove examples of use
Update Metric class API and subclasses
Returns proper ts dataset in each metrics subclass
Add examples of use and minor changes
Rename Metric class
Merge pull request #24 from jgbarah/feature-timespan

Added get_timespan() function.
Removed duplicated class.
Merge branch 'master' of https://github.com/VizGrimoire/GrimoireLib
Added new method to data source to get the SQL query builder object for the data source.
Needed in the new metric architecture.