Add the packaging metadata to build the serpent snap

[come-maiz]

This package will let you publish the latest serpent in the Ubuntu store, and from there reach many users on all the supported Ubuntu versions, and more Linux distributions in progress.

[come-maiz]

Hello!

Here at ubuntu we are working in a new packaging and delivery system. If you haven't heard about snaps before, here's a lot of info: https://snapcraft.io/

I'm very interested in getting more blockchain snaps into the store, and I think it could be very useful for you too because while serpent is on early development you can put it in the edge channel, where the ubuntu community of testers and your early adopters will be able to get it easily, and provide feedback. We can easily automate the delivery of new versions with travis, and then the testers will get a new version as soon as the change is landed in master.

Then, when you are ready to make a stable release, you move the snap to the stable channel and it will be accessible there to the millions of ubuntu users, and many more users in the other Linux distributions that support snaps.

To test this in an Ubuntu 16.04 machine:

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

(--dangerous because the snap you build doesn't come signed from the store. Once you publish it, your users will just have to do sudo snap install serpent).

If you have any questions, please let me know.

pura vida.