Make our CI great

Currently, I have a basic attempt to have an CI running for libotr, it builds libotr and runs the tests.

What would be nice to have is to have is to test on the following platforms:

Windows (appveyor)
Linux (CentOS and Debian?)
Freebsd/Openbsd (I have a VM for openbsd)

Linux could use Docker containers, it would be nice to make 1 Docker container that has all the necessary dependencies already installed so we could just focus on building libotr/pidgin-otr.

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