Recursively evaluate a BLOCK over a list of data structures (locally setting $_
to each element) and return the list composed of the results of such
evaluations. $_ can be used to modify the elements.

Data::Rmap currently traverses HASH, ARRAY, SCALAR and GLOB reference types and
ignores others. Depending on which rmap_* wrapper is used, the BLOCK is called
for only scalar values, arrays, hashes, references, all elements or a
customizable combination.