Improve consistency/spelling in some comments (#924)

Improve consistency/spelling in some comments (#924)

* [comments] Fix incorrectly spelled verb "set up"

* [comments] Fix incorrectly capitalized "MIME" (as in MIME types)

* [comments] Fix inconsistent spelling: "filename" vs "file name"

* [comments] Add missing whitespace

* [comments] Make a comment capitalized like its sibings

* [comments] Improve sentence clarity with a comma

* [comments] Fix inconsistent spelling: "Esc" vs "Escape"

* [comments] Improve consistency of spelling and spacing

* Change 'set up' to 'set-up'