Make all Error

[mantzouj]

I got an error about sqrt "not declared in this scope" in file classifier.hpp. I'm guessing that we need #include <math.h> at the top for it to compile?

[tnugent97]

Similarly I get this error on mac:

inc/video_to_spikes.hpp:87:31: error: call to 'abs' is ambiguous
                double change=std::abs(lum_curr-lum_new);

Which I think can be solved by adding #include <cmath> to the relevant header