Refactor tide.py

[sam-cox]

This is definitely the messiest module, although to some extent that's because it's the most complex. It would be nice if it was a little more pythonic - I'd like it to read more like pseudocode. There are also some rather long lines, and fairly long methods. Could probably also do with factoring out the isinstance stuff which lets you pass datetimes or hours and values or lists of values etc.

[naught101]

Before refactoring, it would be worth running it through pylint/flake8. Python code shouldn't use tabs, and there are some other whitespace issues like spaces after #s that it would make sense to deal with first, in one go.