Change recursive function to while loop to save stack space

[RyanGrange]

Description

Update for issue 87. Removes need for tail recursion call in FindGCDEuclidean and reduces stack pressure.

Checklist

• [X] An issue was first created before opening this pull request
• [X] The new code follows the contribution guidelines
• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [n/a] I have made corresponding changes to the documentation
• [X] My changes generate no new warnings
• [n/a] I have added tests to ensure that prove my fix is effective or that my feature works
• [X] New and existing unit tests pass locally with my changes

[RyanGrange]

Sorry. I screwed up. This was supposed to be a separate pull request with the third commit. I'll cancel this and redo them as branches on my end to avoid this mistake.