Edits to part 2 of the transformer series

[bradcray]

This PR represents my editing pass over part 2 of the transformer series, where most of the edits are minor wording or typographical changes. Some of the more significant changes I made include:

• shortening the summary to get it to fit on one line (hopefully without throwing away key content)
• adding hyperlinks to the previous article at key places
• moving the paragraph of text in the "Result of Forward Pass" section to the front of the section to start with some narrative rather than figures (I think it's OK for it to refer to figures that are about to appear)
• changing memory to heap in discussing the thread allocation overhead to better clarify the cause of overhead since stack-allocated is still allocating memory

Once Thitrin reviews, I'll do one more pass for showstoppers, broken links, spelling mistakes, etc. and then publish.