core: revert previous settings

This reverts commit 7a1fc895.

A matrix with a single column should be considered as classic np.array

Fix potential bug introduced in 2.0.0

Fix issues for Windows

Fix issues when compiling in Release mode

It was causing useless memory allocation

There is a shift in memory that I cannot understand in release mode

Switch to np.array type by default

Remove ${PROJECT_NAME}_export 

Expose Eigen::{LLT,LDLT,QR,EigenSolver,...}