Event tags

TODO:
    list_events:
        filtering of events

    test for:
        _get_date
        list_events:
            multiple events
            tags
Tags should be frozensets

TODO:
    list_events:
        filtering of events

    test for:
        _get_date
        list_events:
            multiple events
            tags
Tests for list_events

TODO: filtering
renamed list_events to get_events

This makes sense as it doesn't actually return a list.
timestamp conversion moved to its own module

TODO:
    filtering for get_events
    move events to its own submodule
    move functions to their own submodule
    tests for convert
Event moved to its own module

TODO:
    filtering for get_events
    move functions to their own submodule
    tests for convert
    move tests for Event into its own file
Event tests moved to their own file

TODO:
    filtering for get_events
    move functions to their own submodule
    tests for convert
Moved functions, constants to their own submodules

TODO:
    filtering for get_events
    tests for convert
    move tests for functions
renamed test_plan -> test_functions

TODO:
    filtering for get_events
    tests for convert
    move tests for functions
extra space in __init__.py

TODO:
    filtering for get_events
    tests for convert
    move tests for functions
test_functions using proper paths

TODO:
    filtering for get_events
    tests for convert
testing for items exposed by plan

TODO:
    filtering for get_events
    tests for convert
basic tests for convert

TODO:
    filtering for get_events
    probably some timezone edge cases for convert