core: make np_type static thhrough a Singleton

core: fix dimensions of vecrtor for Array conversion

Related to #63

Add helper to expose types

Registration

Restoring previous removed code

Fix SEGV with Python 3.

Set the main lib name according to PEP 3149

Change license to be BSD-2-Clause

submodules: use https address

sync submodule, fix python interpreter & libs versions handling, fix #50

core: fix checking of dimensions

Handle conversion from Eigen::Matrix to numpy.array or numpy.matrix

Fix wrong message error

This follows issue #44.