FILTERS: Add Moog lowpass building block filter

This is a basic C++ implementation, including basic tests.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
FILTERS: Add Moog filter C++ implementation

This is a basic C++ implementation, including basic tests.

Fixes #2 and #1.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>