Show overview of all TopGit-tracked topic branches and their
up-to-date status ('0' marks that it introduces no own changes,
'D' marks that it is out-of-date wrt. its dependencies,
+ '!' marks that it has missing dependencies (even recursively),
'B' marks that it is out-of-date wrt. its base).
TODO: Speed up by an order of magnitude
TODO: Some infrastructure for sharing topic branches between
repositories easily
+TODO: tg depend for adding/removing dependencies smoothly
+TODO: tg tidy for creating a one-commit-per-patch tidied up history
+ (for pulling by upstream)
IMPLEMENTATION