Add vale rules and fix errors
Adds the following vale rules:
`.vale/handbook/MergeConflictMarkers.yml`
`.vale/handbook/RelativeLinksDoubleSlashes.yml`
`.vale/handbook/Repetition.yml`
`.vale/handbook/Uppercase.yml`
`.vale/handbook/Zip.yml`
Normally, we'd try to only add 1 rule at a time, but in this case, all errors are from Repetition.
Part of #151 (closed)
Edited by Cynthia "Arty" Ng