Closes #480
'CPU mask' link in Initialization 7 is double-bracketed. 'Previous part' links in SyncPrim 3 & 4 have two opening brackets and one closing. 'Previous part' link in SyncPrim 4 points to current page, instead of previous. Append to contributors.
Some of the code blocks in `SyncPrim/sync-4.md` were missing their end markers, causing normal text to be added to the code block. Fix that.