+ corresponding bits in golang.testing package.

py.bench description follows:

"""
py.bench, similarly to py.test, discovers bench_* functions and Bench* classes
and then runs each discovered benchmark via golang.testing.benchmark. Similarly
to `go test -bench`, benchmarking results are printed in Go benchmark format.

For example, running py.bench on the following code::

    def bench_add(b):
        x, y = 1, 2
        for i in xrange(b.N):
            x + y

gives something like::

    $ py.bench --count=3 x.py
    ...
    pymod: bench_add.py
    Benchmarkadd    50000000        0.020 µs/op
    Benchmarkadd    50000000        0.020 µs/op
    Benchmarkadd    50000000        0.020 µs/op
"""

The implementation is based on t/py.bench from Wendelin.core - see
following commits for its history:

lab.nexedi.com/nexedi/wendelin.core/commit/51f252d4
lab.nexedi.com/nexedi/wendelin.core/commit/074ce24d
lab.nexedi.com/nexedi/wendelin.core/commit/ed13c3f9
lab.nexedi.com/nexedi/wendelin.core/commit/fc08766d
lab.nexedi.com/nexedi/wendelin.core/commit/5a1ed45a
lab.nexedi.com/nexedi/wendelin.core/commit/bcab1246