implement deployment stage

Fixes #7. Implements an initial deployment stage that sends a newly built public/ directory to the web-root.

There is still a little fixme in there: remote files are overritten, but files that do not exist locally anymore are not removed from the remote directory, i.e. if we were to rename / delete pages in a later release, the old files are not removed.

Unless we find a proper rsync style solution to this, another option would be to list all local files with find and all remote files with ftp (or similar commands), compute the deltas locally and remove remote files via ftp again. Cc: @burgardj any ideas?