[C++] Make PyMatrixType a singleton to avoid multiple instantiactions to avoid dynamic linking errors

Improve the packaging of EigenPy

Add Scalar template argument to UnalignedEquivalent struct.

* It allows creating unaligned equivalent of Eigen matrix using a
  different scalar type. This can be useful when matrix types use
  single precision floats, whereas Numpy matrix types use double
  precision floats by default.
* Default template argument value is Matrix D scalar type to preserve
  backward-compatibility.

Fix issue in .pc file

[C++] Add variadic macro to specialize boost python allocator for str…

Enable alignment between Eigen matrix and Numpy matrix

[C++] Add variadic macro to specialize boost python allocator for struct and make data aligned in memory

Fix bug under Mac OS X 

[Bug fix] Remove the pragma line leading to error with gcc 4.8