Improve timestamp handling

[ashmastaflash]

Improve timestamp handling:

Add a synthetic column for handling timestamps. This will add a column to output which will be a python datetime object (composed from ts_sec and ts_usec).

Provide functionality to make time-related queries using a Python datetime object instead of having to reduce query args to two timestamp-related fields.

Add the ability to query using ISO 8601-formatted timestamp. Prioritize so that if multiple timestamps are provided with kwargs, the priority (in order of importance) should be:

1. ts_sec, ts_usec
2. datetime object
3. ISO 8601