Write wrapper function around aesara.scan with nice, intuitive signature

[michaelosthege]

We can just take a bunch of kwargs with informative names and docstrings, and behind the scenes feed things into the less intuitive parts of the aesara.scan signature such as the output_info kwarg.

@ricardoV94

[twiecki]

Could it be a decorator for a function that's executed inside the loop?

k = tt.iscalar("k")
A = tt.vector("A")

# Compute A**k
@aet.for_(k)
def loop(result=0):
    result += result * A
    return result