Make code consistent in formatting

[mhpob]

Mainly consistency in using = vs <-, as well as tidying up some indentations.

[benjaminhlina]

How are we feeling about function and variable names e.g., COA_Standard() with arguments nind vs. n_ind. There wouldn't be any name changes to functions or variable names just reformatting. See https://mc-stan.org/docs/2_18/reference-manual/variables-section.html.

[mhpob]

Is this in the Stan code or R code? If it's in the Stan code then it shouldn't be an issue to change since it's not user-visible, so no changes to the API. If it's the R code we'll probably need to deprecate the old arguments for a time period. Probably overkill since not many people are using this package, but it would be the nice/"best-practices" thing to do.

[mhpob]

Following on from that, I think it'd be good to move to the "tidy" naming conventions (lower, snake case) and maybe shorten some names. Could possibly wrap the old function name (something like coa(z){COA_Standard(z)} if we were to rename that to "coa") and deprecate it after a while.

[benjaminhlina]

This has been completed in #23 and #20. Other issues brought up here will be handled in Trackyverse's version