Tapestop effect that works over any number of cycles

[hellocatfood]

Describe the function/feature you'd like
A tape/record stop effect can already be achieved by running the code d1 $ sound "alphabet" # accelerate "-1". However, this slows down the sample over one cycle. A feature I would like is for the sample, regardless of length or current cps/bpm settings, to be able to have the "tape stop" effect over a number of cycles.

For example, the code could look something like

d1 $ sound "alphabet" # tapestop 1 - this would sound similar to d1 $ sound "alphabet" # accelerate "-1"
d1 $ sound "alphabet" # tapestop 5 - the sample would slow down to a stop over five cycles

Of course, this could raise the question what happens if the user specifies a negative value e.g. d1 $ sound "alphabet" # tapestop "-1". In this scenario I suggest the sample speed up to an arbitrary value to the point where any change cannot really perceived.

[yaxu]

Paging @telephon ! (Probably more of a https://github.com/musikinformatik/SuperDirt/ issue)