Fix a few typos in docs/comments/strings

Fix a few typos in docs/comments/strings

Fixes a few minor typos revealed by running a spell-checker [1] over the
repo. It also identified 'auxilary' -> 'auxiliary', but it's
consistently spelled throughout the code and this patch is limited to
changes to docs, comments, and string literals.

[1] https://github.com/client9/misspell