Bind benchmark builder to Python

[AntoinePrv]

The following PR Close #1038

• Bind TimeUnit and BigO
• Bind internal::Benchmark
• Modify RegisterBenchmark to return the benchmark object
• Bind builder methods from internal::Benchmark
• Add a Python decorator option to use the Benchmark options.

Example

@benchmark.register
@benchmark.option.range_multiplier(2)
@benchmark.option.range(1 << 10, 1 << 18)
@benchmark.option.complexity(benchmark.oN)
def computing_complexity(state):
    while state:
        sum(range(state.range(0)))
    state.complexity_n = state.range(0)

Todo

• This builds on Bind more State methods/attributes to Python #1037 so preferably merge the other one first
• the multi-threaded benchmark is currently segfaulting and needs to be fixed

[AntoinePrv]

Ok, so indeed I cannot run Python in multiple thread without acquiring the GIL.
I tried to register the threads and acquire the GIL, but it now deadlocks.
Probably due to

In a multithreaded test (benchmark invoked by multiple threads simultaneously), it is guaranteed that none of the threads will start until all have reached the start of the benchmark loop

Anyways, seems to be out of scope for this issue

[dmah42]

We should probably update the __version__ in init.py too with this change.

[AntoinePrv]

I rebased on master and bumped version to 0.2.0. I also fixed an indentation bug that arose in the setup.py.

[dmah42]

i fixed this same issue in #1041 :)

well spotted!

[dmah42]

LGTM but i'll wait a while in case there's any issues raised.