Fixing Baha'i Calendar

[bchurchill]

In 2014 the governing authority for the Baha'is, the Universal House of Justice, decided to implement previously unspecified details for the Baha'i (Badi) calendar. As a result, the date for Naw Ruz changed, and is now based on the moment of the Spring equinox in combination with the time of sunset in Tehran. This PR implements:

• the updated version of the calendar
• updates the documentation to address and close #13
• adds new test cases for the Baha'i calendar

For reference, the following specifications were used:

https://www.bahai.org/library/authoritative-texts/the-universal-house-of-justice/messages/20140710_001/1#174438046 https://www.bahai.us/events/holy-days/

[fitnr]

This looks fairly good. I'll need a little time to review. My first inclination is to generalize the solstice-finding function and move it out of bahai.py

[bchurchill]

Thanks! Yeah, take your time. The solstice finding function actually belongs to a dependency (pymeeus). The only reason bahai.py has some special logic for that is because in the Baha'i calendar, the date of Naw Ruz can be a day before/after the spring equinox depending on when sunset is in Tehran.

[fitnr]

I've collapsed your changes into one commit and merged the results. This is now published in v2.2.0