`calc_es50()` supplement documentation; rename `calc_metrics()`?

[bbest]

Need to document other metrics calculated:

https://github.com/marinebon/obisindicators/blob/37c99c776b94e5e29176290496d85e6855d07782/R/analyze.R#L43-L53

[7yl4r]

need to update docs on analyze function

• describe shannon, etc in doc for the function