English copy editing

Mostly adding in appropriate articles (a, an, the).  A few of these edits
are stylistic, not necessary for correctness, but I think it reads a bit
better this way.
Clean up HTML

It's preferable to use <p> than <br> to separate paragraphs, and use
headings rather than <b> to indicate the heading of a section.
Merge pull request #1 from lambda/master

Clean up English and HTML