json: implement {filediff} template Single letter properties are used to keep payload size down, as diff representation can be quite large and longer property names can create a lot of extra work for parsers. Rename is not yet captured. This can be done in a follow-up.

hgweb: expose raw line numbers to templates Surpringly, the templates didn't receive an unmodified version of the line numbers. Expose it to make implementing the JSON templates easier. In theory, we could post-process an existing template variable. But extra string manipulation seems quite wasteful, especially on items that could occur hundreds or even thousands of times in output.