Added nondet-generator option

[rafaelsamenezes]

Description

This adds an option to specify a nondet-generator. If the flag is not set then the combination will be used.

Closes #43

Type of change

• [X] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Manually executed with --nondet-generator fuzzer and --nondet-generator symex and looked over logs

Checklist:

• [X] My code follows the style guidelines of this project
• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [ ] ~I have made corresponding changes to the documentation~ No need to change the docs
• [X] My changes generate no new warnings
• [ ] ~I have added tests that prove my fix is effective or that my feature works~ We need to have a new way to support testing argument testing
• [ ] ~New and existing unit tests pass locally with my changes~ We need to have a new way to support testing argument testing
• [X] Any dependent changes have been merged and published in downstream modules