Setup CI infrastructure

[phrohdoh]

Ideally Travis and AppVeyor would produce native binaries (via GitHub Releases) for GNU/Linux, macOS, and Windows (10?).

[phrohdoh]

AppVeyor integration appears to be complicated by the fact that this repository is under a GitHub organization instead of a user account.

See here for more details.

[phrohdoh]

See easage#1.