Make LibShell ignore all characters in a line after an unescaped # symbol

[dther]

This allows shell scripts to be slightly more portable between Libterm and the full Unix terminal. I have a lot of heavily commented shell scripts that I use to process notes, and being able to use them in Libterm without needing manual editing would be great.

As an aside, thanks for making this! There are lots of things that I want to automate on my iPhone but can't, because I'm not an iOS developer.