BUILD: Propagating changes found when working on sandbox project

This is actually regarding target-specific flags behaviour with MSVC,
and warnings removal in external code
SYNTH: Fixed filter Q lower bound

A value of 0 lead to signal issues and offers no advantages whatsoever.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
MATHS: Added a "SgnNoZero()" function and exposed it in tests

This function is a custom Sgn() which outputs 1 when the input is null.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
TESTS: Fixed zero crossings detection by using new custom sign function

Zero crossings are no longer dedoubled when the input is exactly on zero.
Fixed #76.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
TESTS: Hardened Adsd tests

The fixed zero crossing detection function allows us to harden a bit Adsd
slope-related tests.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
TESTS: Faster debug tests

Performance tests are still useful even in debug for now as they cover
the full synthesizer behaviour.
However they do not need to be so long.
Fixed #70.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
SCRIPTS: Added an utility function for output to wav, using it

This one rely on SciPy.

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