API: Convert EPIE to RPIE

Purpose

Add RPIE implementation.

Closes #142

Approach

Converts the EPIE implementation into an RPIE implementation because EPIE is a special case of RPIE. Also adds RPIE style regularization to the ADAM updates.

Worked with A. Tripathi to develop this RPIE update for the case when there are multiple illuminations:

$o^\prime_{j\bf{r}} = o_{j\bf{r}} + \frac{ \sum_p\sum_j P^*_{pj\bf{r}} ( \psi^\prime_{pj\bf{r}} - \psi_{pj\bf{r}}) }{ (1 - \alpha) [\sum_p\sum_j |P_{pj\bf{r}}|^2] + \alpha [\sum_p\sum_j|P_{pj\bf{r}}|^2]_{max} }$

Where p is the number of illumination, j is the number of scan posiiotns.

Pre-Merge Checklists

Submitter

[x] Write a helpfully descriptive pull request title.
[x] Organize changes into logically grouped commits with descriptive commit messages.
[x] Document all new functions.
[x] Click 'details' on the readthedocs check to view the updated docs.
[x] Write tests for new functions or explain why they are not needed.
[x] Address any complaints from pep8speaks.

Reviewer

[x] Actually read all of the code.
[x] Run the new code yourself; the included tests should make this easy.
[x] Write a summary of the changes as you understand them.
[x] Thank the submitter.

AdvancedPhotonSource / tike