Reusable stacks

[aviramha]

Hey!
First of all - awesome library, really useful for our project!
Second - we have a use case where we need to use a different stack then the one we execute it, but we don't want to create a new stack each time, so I thought maybe we would allocate it once then re-use it. I was wondering if you'd accept a PR adding this functionality.

[nagisa]

I would imagine using the psm library may suit your needs better in case you need precise manual control of the details, but I’m definitely happy to see improvements made to stacker as well.

In particular, some sort of a mechanism that caches and reuses previously allocated stacks would be very interesting and desirable I believe.

[aviramha]

@nagisa You have amazing timing - I just submitted a PR. I think the overall structure makes more sense (building blocks wise) and it solves my issue (I can create a stack and "run" on it)
The possibility of caching is easier to implement using it but currently out of scope in regards to our current desires/needs..