Added InverseFORM

Added the InverseFORM (Inverse MPP) search as specified by Du 2005.

Description

Wrote the InverseFORM class, algorithm, documentation, tests, and examples. The examples and tests were taken from the existing FORM tests and the Du 2005 reference.

Motivation and Context

The InverseFORM algorithm was needed for a research project in SURG.

How Has This Been Tested?

This has been tested by comparing the expected type inputs/outputs, the expected errors, and tested for numerical accuracy using the examples in Du 2005.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

[ ] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Go over all the following points, and put an x in all the boxes that apply. If you're unsure about any of these, don't hesitate to ask. We're here to help!

[x] My code follows the code style of this project.
[x] My change requires a change to the documentation.
[x] I have updated the documentation accordingly.
[x] I have read the CONTRIBUTING document.
[x] I have added tests to cover my changes.
[x] All new and existing tests passed.

SURGroup / UQpy

Feature/inverse form #225