Make the script exit early if any command fails.  Fixes #5
Merge pull request #6 from OpenTreeMap/fail-early

Make the script exit early if any command fails.  Fixes #5
Sourcing the virtualenv fails during provisioning.

Everything used the full path to the virtualenv versions of tools anyways,
and sourcing the virtualenv does work later when you vagrant ssh, so I'm
just removing it.
Merge pull request #4 from OpenTreeMap/support-windows

Vagrantfile supports Windows. Readme has example of create_instance.
Improve Windows support

* Symlink `/etc/nginx/sites-enabled/otm` directly rather than via `configs`
* Use correct syntax for rsync excluded folders
* On subsequent `vagrant up`s:
    * avoid clobbering nginx configuration by ignoring `config` directory when rsyncing `.`
    * use true (non-rsync'd) shared folder (and copy in `local_settings.py`)