Add the packaging metadata to build the partcl snap

[come-maiz]

This is a package for the secure installation of apps that works in most Linux distributions.
Landing it upstream will enable builds that then can be distributed to many users through the Ubuntu store.

[come-maiz]

Hello! I found this very interesting, and I used to quickly test the latest snapcraft release. It worked nicely, so I thought you might like to release your tcl interpreter into the Ubuntu store.

You can find more information about snapcraft here: http://snapcraft.io/

To test it in an Ubuntu 16.04 machine:

$ sudo apt install git snapcraft
$ git clone https://github.com/elopio/partcl
$ cd partcl
$ git checkout snapcraft
$ snapcraft
$ sudo snap install *.snap --dangerous

(dangerous because the snap you build yourself doesn't come signed from the trusted store. Once you push it to the store, your users will just have to do $ sudo snap install partcl)

If you have any questions or comments, please let me know.