Add Support for Days and Months about villager

[ThomasThelen]

And just to note-this can probably be done with a few functions (should't take a huge amount of time and there's already a library that does this in R; https://github.com/edgararuiz/maya

We can definitely use that library and contribute to it to include things that we need-but we'd at the mercy of the maintainer's opinion and time schedule.

There are a number of reasons to do it in-house:

1. We don't depend on someone else's schedule/opinion as to what we can do (for example, if we want to tie an event to a particular day/event, and we're using the library exists-what do we do if the maintainer doesn't like that idea?)
2. Adds to our 'suite' of computational mayan software

There are also a number of reasons to use the existing library:

1. The person who made it works for RStudio
2. He also co-authored the dbplyr library
3. He also wrote a library for the Gregorian calendar, which we'd probably want to use
4. It has an MIT license, so we can always fork it and do what we want with it (keeping the MIT license)

We also don't know until we ask! So I think it's worth jotting down exactly what we want to do with Mayan date times and then taking the considerations above and making a decision