Grammatical Improvements and Gender Neutrality

[rbarnes]

The attached patch fixes a few grammatical errors that I found in the documentation.

Further, it makes an effort to bring gender neutrality to both the code comments and user documentation. Numerous instances of "he", "him", and "his" were converted to "they", "them", and "theirs". Significantly less numerous uses (only one) of "she", "her", and "hers" were converted as well. Pronouns referring to specific people and pronouns in licenses were not changed.