Makefile: parametrize vw args; also mention --multitask

[arielf]

No description provided.

[arielf]

For reference, this is the issue I opened in the official vw repo
VowpalWabbit/vowpal_wabbit#4614

My guess is that the leak happens through the full-connectivity of the features via the hidden layer.

Since the full connectivity is a done-deal (imposed at the start of run by the fact we want a fully-connected NN.)

It seems to me that the SGD update should somehow skip updates to weights that have nothing to do with the ones in the example. IOW the skips should be in run-time (rather than initialization time) and should update only those target feature-nodes that are present in the current example (and/or namespace).

Ideally, this skip vs non-skip (current default) should be controlled by a CLI switch.
--respect_namespaces --restricted_update or something like this.