I mean no disrespect to those who wrote the original text modified by this PR, but I think the English can be improved in some cases. I have encountered a few phrases that didn't seem quite right. I tracked them down, then grepped for other instances of similar language. The changes below can be classified loosely as follows:

• Fix singular/plural agreement
• Resolve ambiguous pronouns; e.g., "it"
• Remove hyphens from words that don't have them; e.g., "undone"
• Fix grammar mistakes
• Fix misspelled words, according to my American English dictionary (they may be spelled correctly in other English variants)
• Make English phrases sound more natural (to me, of course!)

This PR is not exhaustive. I am willing to make changes to this PR if you find any part of it objectionable.