Recursively search parent directories for VCS marker directory

When detecting the VCS, the plugin should recursively search the base directory's parent directories for the marker directory.

This functionality is required when a repository has the following layout:

    some_project/
    some_project/.git
    some_project/some_module/
    some_project/some_module/build.sbt
    some_project/etc/
    ...

Otherwise, the release process will fail:

    some_project/some_module $ sbt release 
    ...
    [error] Aborting release. Working directory is not a repository of a recognized VCS.
    [error] Use 'last' for the full log.