Operations on Stretchy Vectors

add!   stretchy-vector new-element  => stretchy-vector	[G.F. Method]

add! adds new-element at the end of stretchy-vector. The result is == to stretchy-vector, and stretchy-vector is destructively modified by this operation.

remove!   stretchy-vector element #key test count  => stretchy-vector	[G.F. Method]

The result of remove! on a stretchy vector is == to stretchy-vector, and stretchy-vector is destructively modified by this operation.