Use Composer script, fixes #1

[hlubek]

Move custom wrapper script to a Composer script to have it in ´bin/prunner` (like expected for a Composer package) and errors on install.

Question: Calling bin/prunner outside of the project root doesn't work correctly with this approach. Does this matter for us?

[Benjamin-K]

@hlubek We are running prunner from outside this package. As i understand your PR correctly, this will no longer be possible, right?

[hlubek]

@Benjamin-K Hi, this is only about the script that is being managed by Composer and needed some special workarounds with composer.json until this PR. The script that will be installed in [project root]/bin/prunner needs to be called from the project root.

The Prunner process itself can still run outside of this package as before.

[christoph-daehne]

This might relate to FEATURE: connect to existing Prunner system service. The Prunner binary is no longer installed via composer (opt-out).