Use travis-ci as continuous integrator with builind for the following
operating systems:
- ubuntu 16.04; build with gui and without gui
- macOS 10.14, 10.13, 10.12, 10.11 with macports
This file can be used as build dependency tracker to avoid duplicated
information.
TODO:
- windows 10
NOTE:
- ubuntu 18.04 is not supported yet. Azure pipelines has the same
limit.
[1] http://travis-ci.org
