contrib: new script to read events from a named pipe and emit catapult traces I'm starting to get more serious about getting some insight into where we're spending our time, both in hg itself but also in the test suite. As a first pass, I'm going to try and produce catapult traces[0] that can be viewed with Chrome's `about:tracing` tool. 0: https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/edit#heading=h.nso4gcezn7n1 Differential Revision: https://phab.mercurial-scm.org/D4342