Support git-describe

[nathansgreen]

maven-git-commit-id-plugin supports git-describe. In particular, it supports marking "dirty" working copies, so it's clear whether a given build was from a completely clean checkout. Any modification to a committed file will produce a dirty state, leading to a build that may not be reproducible.

[izeye]

@nathansgreen @n0mer Resolved via #32 ?

[n0mer]

@izeye @nathansgreen fixed in 1.4.18

[tha2015]

I compared the generated value for git.commit.id.describe and the values from "git describe" command and the git-commit-id-maven-plugin

The "git describe" command and the git-commit-id-maven-plugin generated the same value and they are different to the value from this Gradle plugin. So I'd like to reopen this issue to review/update the implementation for git.commit.id.describe to make sure we are generating the same value as "git describe" and git-commit-id-maven-plugin.