[unittest] Add test returning reference of std::pair

[std-map] add more general visitor for map types

+ test boost::unordered_map
+ pull StdMapPythonVisitor out of eigenpy::python namespace (shouldn't exist, add using-decl for backwards compatibility)

Add helper for type_info

Add bp::dist to std::map converter + unittest

[std-vector.hpp] make std::vector allocator type a template parameter for exposeStdVectorEigenSpecificType

[std-vector.hpp] make std::vector allocator type a template parameter for exposeStdVectorEigenSpecificType

Nix

Fix function signature on Windows