Note: current mail notifications are configured for first tests.
We may need to reconfigure this later.
See build logs at https://travis-ci.com/fltk/fltk
This implementation differs from existing fltk-test and also gitlab implementation :
- minimum, fast light implementation: stripoped all unused constructions compared to other implementations
- supports successful builds of four targets (linu, osx and then gcc and clang for each of them)
- uses before_script instead of before_install
- uses after_success for building documentation, instead of building always if error
- only builds documentation on linux targets for now (can easily change if future)
