Adds support for named period ranges
See #2
Example period formats (for evaluators such as the Sumo Logic evaluator):
-10m to -5m
is 10 minutes ago to 5 minutes ago-1h to 0h
is hour ago to now-1d to -1h
is 24 hours ago to 1 hour ago- [NEW]
today
is from 00:00AM until now - [NEW]
yesterday
is from 00:00AM yesterday until 00:00AM today