Vector and list with two template parameters

[molpopgen]

Rationale:

• STL containers take a type and an allocator as template params
• Current .pxd files rely on the default allocator
• There are better-performing allocators out there (boost, Intel's TBB library, etc.)
• These new .pxd files seem to be the "best we can do" as Cython doesn't support template type parameter defaults.

The downside is that cimports need to be careful about name conflicts, but "cimport x as y" solves that.

[robertwb]

How about building on top of 767fce8

[molpopgen]

I'm going to close this PR and open a new one, starting clean from current Cython master.