v0.0.2b4: Merge pull request #39 from abyrne55/v0.0.2

Metric class changes:

• oldest_date_datetime changed input type, it can either be a datetime object or a timedelta object.

PrometheusConnect class changes:

• start_time and end_time parameters don't accept strings any more, they can only be datetime objects.
• similarly chunk_size parameter can only be a timedelta object

utils.py added

• These are some utility functions that are not needed for the core functionality of the library, but come in handy when parsing strings for datetimes or timedeltas.