Metafacture Core Distribution 6.0.0

We switched to Java version 11.

Changes

New Features

• IO: Open gzip compressed content from HTTP #511

Bug fixes

• IO: Fix misconception of "Content-Encoding" #513
• IO: Close resources #514

Others

• Provide examples for every flux-command #488
• Upgrade Gradle wrapper #520
• Switch to Java version 11 #518