PR 180 + pllim edits (#183)

* added first iteration of focus_diverse_epsfs

* Add files via upload

* made some changes based on initial feedback

* added .rst file for focus_diverse_epsfs

* fixed remaining PEP8 issues

* docstrings now better match other acstools modules

* updates incl. docstrings, trailing / support, etc.

* Lim edits

* Fix bandit and doc failures

* Address review comments

* Fix docstring formatting

* Suggested change by Gagandeep and Jenna

to clarify this option

* Apply Gagandeep fixes to indexing

* Remove trailing whitespace

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Co-authored-by: Gagandeep Anand <30330521+gsanand@users.noreply.github.com>
Co-authored-by: Yotam Cohen <ycohen@stsci.edu>