Implement Effective Temperature module from ladybug legacy code

[chriswmackey]

As many ladybug legacy users know, @stgeorges did a phenomenal job writing code for calculating effective temperature and apparent temperature in ladybug-leagcy. At this point, it would be great to further clean + document this code and and integrate it into ladybug-comfort such that other developers can easily calculate effective and apparent temperature using the ladybug-comfort package on PyPI and view documentation about the model within the online documentation for this repo.

You can see that I have already done an example of translating one of the models from @stgeorges 's components with the Heat Index (HI) in this library. This was translated over from the heat index function in the thermal indices component and the references in the docstring came from on the wikipedia page for heat index.

I am posting this issue here in the event that someone sees it and decides that they would like to take up the mantle of transferring this code, documenting it, and getting it to conform to PEP8. If anyone has interest, please feel free to post on this issue.

[chriswmackey]

As an additional note to a question @janeliutw brought up, I think that Effective Temperature should be broken down into two methods:

1. For effective temperature (ET or TE)
2. For radiant effective temperature (RET or TRE)