Check for a zero-element character vector return from readChar.  (This
is not documented as the EOF return value, no, but it makes sense).

Also commit bug reports #18 and #19, and some README rearrangement.

Link to them from README for webby goodness.  (Actually for webby
goodness I have to call them BUGS.org and TODO.org, *sigh*).

In particular, be careful not to overclaim.  Motivated by preparing to
announce to the ESS mailing list.