[REQUEST] Support command-line release of JAR file

[barbeau]

Is your feature request related to a problem? Please describe.
Currently, the release process is very manual:
https://github.com/MobilityData/gtfs-validator/blob/master/RELEASE.md

This process is labor intensive and prone to mistakes.

Describe the solution you'd like
We should be able to support a command-line release such as mvn deploy or gradlew assembleRelease. This allows for a simpler release process that is less prone to errors and could eventually be used to build releases automatically via CI and Git tags.

We should also support minification to try and reduce the size of the output JAR file.

Gradle plugins to investigate:

• https://github.com/johnrengelman/shadow

Describe alternatives you've considered
Do nothing - leave release process as-is

[ghost]

I'd suggest we avoid using Maven as to keep things streamlined around Gradle

[barbeau]

@Fabrice-V Yes, if possible, I agree - I only intended the mention of mvn deploy to be an example of a general command to package an application.