Grammar fixes. I have tried to keep as close as possible to the original phrasing and meaning, correcting only for good spelling, grammar and sentence structure. In a few cases I've added a "suggested" re-wording for strings in language.cfg; these are commented out on a nearby line. Please see the diff to get a quick idea of the sorts of changes that have been made.
Merge pull request #209 from sorpigal/grammar

Grammar fixes.