Updates for MediaWiki 1.39

[Kenny2github]

• Fix #109 and its brethren
• Update CREDITS
• Move hook handling into its own class and file
• General cleanup and modernization

Closes #109 Closes #115 Closes #116 Closes #117

[jacob-g]

Looks good on my local for 1.39, now going to test on staging to ensure backwards-compatibility.

[jacob-g]

This is a breaking change.