Use iso8601 library to any of the possible iso8601 date format variation...

Resolves #2

```python3
import iso8601
example_dates = ["2010-01-01T00:00:00Z", "2010-01-01T00:00:00", "2010-01-01T00:00:00.001Z", "2010-01-01T00:00:00.001"]
for example_date in example_dates:
    print(iso8601.parse_date(example_date))
```