Add support for multiple sub-projects in the same Git repo

[eliaslevy]

Would require per sub-project configuration and being able to match the different version tags for each subproject (e.g. foo-v1.0.0, bar-0.5.0) and pass the right glob to git describe --match.

[dwijnand]

I'm hesitant to add this support. For one because I think (but I'm not sure) it goes against what sbt expects.

However if someone can implement this, and the change isn't that big, I might reconsider.

[eliaslevy]

See #62.

[dwijnand]

Fixed by #158

[LeifW]

This doesn't seem fixed at all? dynverTagPrefix is still scoped to ThisBuild, so it can't vary per-subproject.

[touchdown]

This doesn't seem fixed at all? dynverTagPrefix is still scoped to ThisBuild, so it can't vary per-subproject.

yah i just maintain my own jar with this change

-  override def buildSettings = Seq(
+  override def projectSettings = Seq(