MANAGER: Clean the feeder/getter API

Now input feeding and descriptor retrieval are clearly separated.
Part of #38.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
MANAGER: Store the current frame at each feeding stage.

This will allow descriptors to retrieve it later instead of passing
it at each descriptor computation.
Part of #39.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
MANAGER: Fix the case where input data is longer than the default one

This resizing should not happen here but beforehand - analysis frame
length is supposed to be fixed.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
TESTS: Make tests up to date with last API changes.

Part of #38.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
MANAGER: Remove the implicit copy of the computed descriptor

Part of #39: copy of the computed data should be done explicitly
by the user.

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
DESCRIPTORS: Replace all call to GetDescriptorCopy() with explicit copy

Part of #38.

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