Support Mercurial bookmark instead of branch

[slippycheeze]

At work we use bookmarks, not branches, to track work in Mercurial. Your tool is excellent in every regard, except that it only reports "default" as that is the only branch ever in use in Hg. Allowing that to show a bookmark instead would be great!

.hg/bookmarks.current might be useful for extracting this data, or the get-bookmarks option and the %m format.