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When we're doing changes in cookiecutter templates, we often have to
generate an re-generate the project, to check if it's actually doing
what we expect.

I wanted to try making this feedback loop a bit tigher, so I came
up with this.

The idea is, when you're editing the template, use a workflow like:

    make watch

This will run `cookiecutter --no-input . --overwrite-if-exists` right
away, and then every time you change something inside the template
directory.
I was using it while working on #169 and I quite liked it.

There is room for improvements, some things I thought were:

1) it would be nice to re-run the command also when cookiecutter.json
   changes, or any of the hook scripts too (I couldn't figure out how
   to do this properly with `watchmedo`, it only watches directories)
2) it would be nice to support running cookiecutter asking for input
   the first time and then with --replay the following times

What do you think?