revsetbenchmarks: use combination variants in default set Now that we have them, let's make use of them.

revsetbenchmarks: support combining variants with "+" We need more advanced variants in some cases. For example, "The last rev of the sorted version". We introduce a syntax for this: `reverse+last` means `last(reverse(REVSET))`.

revsetbenchmarks: use many more variants by default So far the variants feature was introduced, but not used by default. We now use a set of basic variants by default.

revsetbenchmarks: display even more compact timing result We now use an 8 char display for timing (from 10), we add some logic to drop precision if the number grows too large (as we do not care about sub-0 digit in this case). This allow to pack more variants in a single screen.

revsetbenchmarks: allow running multiple variants per revset The current benchmarks were only testing the whole iteration. This is suboptimal because some changes are meaningful for things like first result, minimum or sorting. We introduce a "variants" feature that let you systematically add some variants to all revsets tested. A typical variants value would be 'plain,min,last,sort'. When testing 'all()' it will also provide testing for: - all() - min(all()) - last(all()) - sort(sort) and output: plain min last sort 0) 0.034568 0.037857 0.000074 0.034238 1) 0.011358 32% 0.020181 53% 0.000080 108% 0.011405 33% Using revsets (who hit the API) instead of the internal API add some overhead, but the overhead should be the same everywhere so it still allow comparison. This is is more simple to implement and allows comparison with older versions who do not have the same API.

revsetbenchmarks: display relative change when meaningful If the time difference is more than 5% from the previous run, we'll display relative information. This makes it much simpler to spot performance changes in a sea of benchmarks.