Refactor .travis.yml

* Make CI figure out overall status early
* Allow not yet succeeding jobs to fail
* Add an after-test PYPI deployment stage
* Run ldconfig only under GNU/Linux
* Run OSX when tagged, triggered manually or by cron
* Add fast failure to install subcommands
* Making python 3.7 + compatible
* Python warning: Using or importing the ABCs from 'collections' instead
  of from 'collections.abc' is deprecated, and in 3.8 it will stop
  working
* Drop sudo: required from Travis CI config
* Keep complete env matrix in tox.ini
* As per @rooterkyberian's request
* Drop deprecated "sudo"-less mode
* Switch Travis CI to xenial having better versions
* Reorder test jobs to run latest first
* Bump python versions for macOS
* Put libyaml version into env var in Travis CI
* Update pyenv formula
* Run Python 2.6 env under Ubuntu Trusty
* Upgrade pypy3 to 3.6-7.0.0 under macOS
* Reduce Python build output under macOS
* Make `set -e` mode more narrow
* Use single quotes in string literals in YAML
3 files changed