A tag command is added to the Git porcelain API. Tests were
also added to stress test the tag command.
Change-Id: Iab282a918eb51b0e9c55f628a3396ff01c9eb9eb
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>