refactor handling of timezones #7
Description
At the moment the tool handles timezones in a mostly ok manner, just not that generically. Ideally, in the WeeWx tradition, all time processing should be done in UTC, and conversion to local time handled at the last second before output processing.
What needs to happen is that there should be a new "pre/post-processor" module that converts the passed time into UTC before passing to any tide generation function. The module could then convert to local as a final step when required.
It should be able to:
- convert a single date time to/from local time from/to UTC
- convert a list of date times to/from local time from/to UTC