annotate: build format string separately from annotation data This prepares for porting to generic templater API. Note that we cannot use '%*s' to pad white spaces because it doesn't take into account character widths, as described in 4f5a6df2af92.

formatter: convert float value to json It will be used to encode ctx.date().

formatter: have jsonformatter accept tuple as value This is necessary for "annotate" to encode ctx.date() in the same manner as jsonchangeset printer. It doesn't support list object because keeping mutable object in _item could be a source of hidden bugs. Also, I can't think of the use case.

formatter: extract function that encode values to json string This is the stub for tuple support, which will be used to encode ctx.date() in the same manner as jsonchangeset printer.

contrib/synthrepo: pass options to ctx.diff as kwargs, not a dict

contrib/synthrepo: only generate 2 parents if model contains merges If `hg analyze` is run on a revision set which contains no merges, then `hg synthesize` will raise IndexError trying to select from p2distance, which will be empty.