Set up automatic versioning

[lbergelson]

We probably want to have the version number be automatically incremented so that it's easy to publish unique snapshot builds and easy to identify which commit produced a specific binary.

Some potential options:

1. ajoberstar/reckon: a gradle versioning plugin with features like publishing to github
2. What htsjdk does now, uses the palantir/gradle-git-version plugin to get a version and then does some other stuff to it.
3. Something completely different

[lbergelson]

I'm pretty happy with how the versioning in htsjdk works now, although it would be nice if it could do some things that the reckon plugin does, like publishing to github release and ignoring non-mainline version tags when determining the version number.

What I want in a version number:
Semantic versioning for releases, + additional information for non-release builds.

examples releases: 0.0.1, 0.1.1-rc1, 1.2.3
example snapshot build: 0.0.1-g4a52d1339-SNAPSHOT

[magicDGS]

I vote for reckon, as the version numbering fits @lbergelson requirements (including the hash/timestamp) and it also allows to publish tagged releases properly to GitHub. Like that, we can also have a proper releasing process with release candidates before doing a release (for early adopters or tests).