No support of log determinant

Created by: laurentes

As said here, determinant computation is subject to underflow/overflow.

When computing log determinant, this might be avoided by directly working in the log domain. In the python universe, we may rely on numpy.linalg.slogdet(). We should consider to provide such a function in the C++ universe.

Currently, the PLDAMachine class may be subject to underflow/overflow.