Add new -today-in-history, -month, -day, and -year search filters

[KarimPwnz]

I have implemented -month, -day, and -year for more general searching (values are parsed through time.parse). Additionally, this PR includes -reminisce which shows entries from today over the years, by modifying -month and -day (this resolves #1143).

However, I did not implement the (_ years ago) output suggested in #1143: it would add too much complexity. Also, the included tests check -reminisce implicitly through -month and -day: I did not find a way to elegantly create journals exactly a year ago.

Edit: I have implemented -reminisce tests—see comments below.

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have tested this code locally.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.
• All tests pass.

[KarimPwnz]

There is some accidental functionality overlap with -on (you can do -on January, etc.); however, -month, -day, and -year are explicit, more general, and can be used in combination. Furthermore, -on is only meant for a single date.

[KarimPwnz]

For testing -reminisce explicitly, we could use unittest.mock.patch on datetime.datetime in a step that creates journals exactly n year(s) ago.

Edit: I ended up using the built-in time.parse in -reminisce and mocking it in tests.

[wren]

This is a promising start.

I put a few comments inline. Once those, and the questions in the issue are resolved, I think we can move this one forward.

Thank you!

[wren]

This looks great. Thank you!

We're just waiting on nailing down the name for the reminisce arg, and then we can get this merged in.

[KarimPwnz]

I've updated the name. I think this is complete now.

[wren]

@KarimPwnz Thank you! I started a new dayjob last week and it's taking up all my time during the week right now. I'll get through every review and issue reply on Saturday. Thanks for your patience!

[KarimPwnz]

Oh, congrats on the job! Do take your time.

[wren]

Looks great! Thank you!