simpleperf: use libevent in record command.

Support read Event in IOEventLoop, test it, and use it
in record command.
Format related code and clean up some comments.

Bug: http://b/30405638
Change-Id: I3b07d50b0374be3f3e7ee9fa4d0c0ccc8ae21a2b
Test: run simpleperf_unit_test.
10 files changed