template: add revset() template function Adds a template function that executes a revset and returns the list of revisions as the result. It has the signature 'revset(query [, args...])'. The args are optional and are applied to the query string using the standard python string.format(args) pattern. This allows things like: '{revset("parents({0})", rev)}' to produce the parents of each individual commit in the log output. If no args are specified, the revset result is cached for the duration of the templater; so it's better to not use args if performance is a concern. By itself, revset() can be used to print commit parents, print the common ancestor of a commit with the main branch, etc. It can be used with the ifcontains() function to do things like '{ifcontains(rev, revset('.'), label(...), ...)}' to color the working copy parent, to color certain branches, to color draft commits, etc.