Add snapcraft build config

[ad-m]

Heroku uses Snapcraft for CLI distribution.

For intern TODO:

• Create flow for package publishing (see CI from snapcraft - https://snapcraft.io/build )
• Update README how to install published package
• Update quick starter on website how to install
• Write rbx-asciicast-gen how to install & use
• Verify the-right-way for package scoping

To build locally:

docker run -v "$PWD":/build -w /build snapcore/snapcraft:stable snapcraft

To instal locally:

snap install ./h1-cli*.snap --devmode

To use installed locally:

/snap/bin/h1-cli login --username karol.bregula@siecobywatelska.pl

SSH authentication works.

$ ls -lah /snap/bin/
razem 8,0K
drwxr-xr-x 2 root root 4,0K cze 23 01:07 .
drwxr-xr-x 5 root root 4,0K cze 23 00:03 ..
lrwxrwxrwx 1 root root   13 cze 23 01:07 h1-cli -> /usr/bin/snap
lrwxrwxrwx 1 root root   13 cze 23 01:07 h1-cli.rbx-cli -> /usr/bin/snap