Automate build using GH actions

[yanntm]

This patch lets us build smart/meddly automatically using GitHub Actions.

It contributes :

• the .gihtub/ folder with the actual build scripts. Critical file is "linux.yml"
• edited some configure.ac and Makefile.am to force static build. This means smart binary is standalone instead of carrying a dependency to libmeddly.so
• minor patch to one file that was blocking compilation

So with this patch, any time we commit to master branch of smart, a binary is rebuilt and deployed to "linux" branch of the repo, ready for download. I do have similar scripts for osx/win if you'd like to have those too.

Have a look at the Actions tab here to get an idea of the result
https://github.com/yanntm/smart/actions
And of course the actual smart binary built here : https://github.com/yanntm/smart/raw/linux/smart

Hope you like it !