Benchmark discovery fails if "./" is not prepended to a relative path

[nicholasjng]

Currently, when having the following example directory structure:

src/benchmarks.py
   /main.py

executing runner.run("benchmarks.py", ...) from inside the src directory results in an importlib error:

Apparently, the ismodule check falls through to the very last import attempt, which fails since the found module does not have a __path__ set.

This is an indication that the discovery branch is backwards - to fix, we can try calling path.is_{file,dir}() on the input first, and only then try to understand it as a module name.

This should be safe since the Python file has a suffix .py, which eliminates collisions between e.g. __main__ (the module name) and __main__.py.

Also, once it's fixed, docs should be updated.