Added maven-shade-plugin to build uber jar with all dependencies

[LumnitzF]

Fixes #10

[agoeb]

Great work! The jar builds, is usable on my machine, and works as expected. I just noticed a few things about the build itself that might need a little improvement:

• There are deprecation warnings about "actions/checkout" and "actions/upload-artifact". Please update the respective versions.
• The UPX action issues a deprecation warning about the "file" parameter and suggests using "files" instead. Could you maybe switch that as well?
• The "build-shaded" step produces an artifact called "target-shaded". To me, "shaded" seems like an implementation detail, and what I am looking for is a Jar. Could you rename the target to "target-jar" or "target-java" please?
• I'd like the Jar to be publicly downloadable, so it might be a good idea to include it into the "release" step. WDYT?

[LumnitzF]

Applied the changes you mentioned.
The final jar is also included in the release step, however I can't/don't know how to test it

[agoeb]

Few further remarks, including an important one regarding job dependencies.
Sorry if I come across a bit picky, but I suppose fixing stuff in the workflow is cheapest while you're at it anyways. :-)

[agoeb]

Thanks a lot!