parser differences.

I've tried to follow mpw's command line parsing algorithm but there are some differences.

Mostly this is because

set q '"' ; echo {q} really "

is equivalent to

echo " really "

mpw removes # comments before shell expansion so this _is_ an error:

echo {q} # "

- mpw doesn't split on ; until after variables are expanded.  I split before variable expansion.
- escape new-line is not allowed in a '' or {} string.
- quote matching happens when the line is read.