Support for drop of multiple elements

[hackaugusto]

Feature request

Quite often when writing MASM we have to move multiple elements around and drop them. To do that it would be useful for the drop opcode to support a bitmask, to determine which values to drop. For example:

push.4 push.3 push.2 push.1 # stack is [1,2,3,4]
drop.0b0101                 # drop the second and forth element, stack becomes [1,3]