First steps towards a metrics using classes approach.
Sample of creating Commit metric.
Added how metric register to the data source.
Metrics are created in Report reading all available.
Implemented the dynamic loading of metrics from modules in "vizgrimoire/metrics" dir.
Implemented get agg and evol data for Commit metric.
Metrics are now added for data sources from Report init.
Merge branch 'metric-class'
read_options included directly in this file.