Pedantically correct spelling in User's Guide

…though it warms my heart that the letter order was reversed in a sentence explaining the reversed order of *Order explanations.
Merge pull request #302 from barnardb/patch-1

Pedantically correct spelling in User's Guide
Correct a few errors in the User's Guide

I can't tell from a quick glance at the implementation whether the bounds of the image of atan2 are theoretically open or closed, so I went with open-closed as it is often defined, even though in practice results can compare equal to -pi.
Merge pull request #303 from barnardb/patch-2

Correct a few errors in the User's Guide