#92 Add archive task configuration to make the build reproducible

[marko-bekhta]

Fixes #92

here's how I've tested locally:

# build with no cache:
./gradlew --no-daemon --no-build-cache clean assemble publishToMavenLocal -Pskip.signing

# calculate md5s:
md5sum build/libs/hibernate-models-1.0.0-SNAPSHOT.jar build/libs/hibernate-models-1.0.0-SNAPSHOT-javadoc.jar build/libs/hibernate-models-1.0.0-SNAPSHOT-sources.jar

# rebuild with no cache again:
./gradlew --no-daemon --no-build-cache clean assemble publishToMavenLocal -Pskip.signing

# calculate md5s again and compare with the previous results:
md5sum build/libs/hibernate-models-1.0.0-SNAPSHOT.jar build/libs/hibernate-models-1.0.0-SNAPSHOT-javadoc.jar build/libs/hibernate-models-1.0.0-SNAPSHOT-sources.jar