lib.tex: add libimp; remove bogus warning about lineii.
libmath.tex: document hypot().
libmd5.tex: rename md5.md5() to md5.new().
libposix.tex: document chown().
libposixfile.tex: openfile() instead of fileopen().
libsocket.tex: document gethostbyaddr().
libtypes.tex: add footnote explaining why readline() keeps the newline.
ref3.tex: correct typos, add back*quotes to index.
ref4.tex: don't use \verb inside footnote.
ref5.tex: explain repr() and str() and add them + back*quotes to index.
ref6.tex: correct typo, don't use \verb in footnote.
ref7.tex: don't use \verb in footnote.