use typedefs and define structs in some places

[dlyongemallo]

I'm not sure why s_type is defined the way it is, rather than using MKL_Complex8 from the MKL?

There are also a couple of places where a parameter or return value is a vector, when maybe it should be a struct.

I think there are also some places where ints should be size_ts or vice versa, to allow compilation on different architectures, but I will need to do some more investigation.

[dlyongemallo]

Grid coordinates should be pair<int> not vector<int>. It should probably be a typedef as well.