use pybind11 and cppimport

[ghost]

Thank you for porting this to C++.

This PR changes the compilation to pybind11 and cppimport.

In this way, it becomes really easy to install and run, e.g. running

cd src/main
python demo.py

will just work (assuming you have cppimport installed): it will automatically compile src/main/cpp/concaveman.cpp and load it.

The code for passing in and returning the arrays also becomes a lot simpler.

Not directly related to this change: I added a DEBUG flag for removing the std::cout printouts, and fixed one compiler warning for a missing typedef.

[ChrisBarker-NOAA]

Nice work!

could this be restructured to use pybind11 and pre-build the all teh code so it would run without a compiler or any other dependencies?

I've done that with Cython (#14) -- because that's what I'm used to -- but pybind11 would probably make cleaner binding code.