Vectorial Envelope Generators

The opcodes to generate vectors containing envelopes are vlinseg and vexpseg.

These opcodes are similar to linseg and expseg, but operate with vectorial signals instead of with scalar signals.

Output is a vector hosted by an f-table (that must be previously allocated), while each break-point of the envelope is actually a vector of values. All break-points must contain the same number of elements (ielements).
