Watch the template and referenced files, and update output every time there's a changes

[kblomqvist]

Like Sass has the following feature

sass --watch input.scss:output.css

I think this would be handy if there's support for Latex (#31).

[nixjdm]

Template watching sounds pretty useful, but I think it should be defaulted off. If the output files are malformed because the template was saved with an error (not even a jinja error necessarily), nasty things could happen. It depends on what the output files are for.