The current implementation of FixtureCommand is a bit quick and dirty.
From time to time we try to decouple as much logic as possible from this.
This time a function parameter has been swapped to a class param
so that we can delegate/swap the loops in the __invoke method some time.

The upcoming feature covers generation of completely random posts.
This does not fit to the current section which only explains the fields.
So we create a sub-section for fields to have siblings for other things.

Lesser test may make CI faster

* No need for wp-cli/entity-command
* Marked supported PHP Version
* Marked lowest possible WP Version (if johnpbloch/wordpress is used)
* Swapped roave/security-advisories to testing where it belongs

* Changes to testing / dropped obsolete things

We use coveralls.io to measure the code coverage over time.
With some release the executable has been renamed so it
didn't uploads coverage.xml anymore in the end.
To prevent this and other possible issues
we install coverals alone and run the executable for '^2.2'.

* .gitignore: Also ignore the coverage file in root dir