identify: add template support This is based on a patch proposed last year by Mathias De Maré[1], with a few changes. - Tags and bookmarks are now formatted lists, for more flexible queries. - The templater is populated whether or not [-nibtB] is specified. (Plain output is unchanged.) This seems more consistent with other templated commands. - The 'id' property is a string, instead of a list. - The parents of 'wdir()' have their own list of attributes. I left 'id' as a string because it seems very useful for generating version info. It's also a bit strange because the value and meaning changes depending on whether or not --debug is passed (short vs full hash), whether the revision is a merge or not (one hash or two, separated by a '+'), the working directory or not (node vs p1node), and local or not (remote defaults to tip, and never has '+'). The equivalent string built with {rev} seems much less useful, and I couldn't think of a reasonable name, so I left it out. The discussion seemed to be pointing towards having a list of nodes, with more than one entry for a merge. It seems simpler to give the nodes a name, and use {node} for the actual commit probed, especially now that there is a virtual node for 'wdir()'. Yuya mentioned using fm.nested() in that thread, so I did for the parent nodes. I'm not sure if the plan is to fill in all of the context attributes in these items, or if these nested items should simply be made {p1node} and {p1rev}. I used ':' as the tag separator for consistency with {tags} in the log templater. Likewise, bookmarks are separated by a space for consistency with the corresponding log template. [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-August/087039.html