Create LDA Change Point package

[ethanwhite]

To facilitate automating analysis for hundreds of communities the core code in Erica's LDA repository needed and turn into a Package. Steps include:

• [ ] determine which files contain core code (need code for determining # of topics, running LDA, and running changepoint model)
• [ ] extract those files (and their commit history) into a new repo
• [ ] streamline code to remove redundancies (we're going to be running hundreds of communities)
• [ ] refactor to create more readable code with well named functions and a master function to rule them all.
• [ ] turn into a package

(Moves over @skmorgane's issue from https://github.com/weecology/macro-ts-struct/issues/1)

[ethanwhite]

This is being/has been done over in https://github.com/weecology/ldats.