mercurial: switch to util.timer for all interval timings util.timer is now the best available interval timer, at the expense of not having a known epoch. Let's use it whenever the epoch is irrelevant.

util: introduce timer() As documented for timeit.default_timer, there are better timers available for performance measures on some platforms. These timers don't have a set epoch, and thus are only useful for interval measurements, but have higher resolution, and thus get you a better measurement overall. Use the same selection logic as Python's timeit.default_timer. This is a platform clock on Python 2 and early Python 3, and time.perf_counter on Python 3.3 and later (where time.perf_counter is introduced as the best timer to use).

color: move the '_render_effects' function to the core module