Support for zsh

[jeduan]

Hi, thanks for the amazing utility.

While trying it I was baffled, since lots of simple tasks fail. For example, both na -r and na -a 'a task' will always return

 na:106: no matches found: /*.taskpaper

While na dir when such dir is found in ~/.tdlist will return

na:107: bad math expression: operand expected at `/Users/jed...'

Looking at this stackoverflow post it looks like some escaping with zsh is the culprit and indeed, manually setting everything up in bash made it work.

Would you consider adding support for zsh?

[ttscoff]

Would you? I've never gotten myself to make time to learn zsh, but if you (or anyone else) want to clean the script up to work in both shells, I'd be happy to merge it in.