Rename MetricStore fire methods: fire_(*) -> fire.\1
Add MetricStore.fire.last
Move MetricStore fire methods' docstrings into their functions (to be consistent with the rest of our function docstrings)
Bring back the dynamic fire aggregation method creation in MetricStore
Merge branch 'develop' into feature/issue-117-add-last-aggregation-method-to-metricstore
Use 'number' instead of 'float' in docs for MetricStore fire methods
Fix bad MetricStore test description: .fire.inc -> .fire.last
Merge branch 'feature/issue-117-add-last-aggregation-method-to-metricstore' into develop