Calculate impact of the trace module about pytest-ekstazi

[Igorxp5]

Wait for #16 be completed.

[Igorxp5]

Forget about #16 for now, see the thread resolution.

[Igorxp5]

Running test of https://github.com/circuits/circuits

Plugin disabled

====== 302 passed, 2 skipped, 1 xfailed, 4 warnings in 190.44s (0:03:10) ======

Plugin enabled

====== 1 failed, 301 passed, 2 skipped, 1 xfailed, 4 warnings in 505.65s (0:08:25) ======

Plugin enabled with minor changes

====== 3 passed, 300 skipped, 2 xfailed, 4 warnings in 13.79s ======

[Igorxp5]

The first usage takes x2.65 more than not using the plugin. But next executions are much faster (x14 less in this example) because it's not needed run the entire test suite.