See Filter::exec, Filter::cpp and Filter::sh for examples of the use of this module.
Note that the size of the buffers is limited to 32-bit.
If a CODE reference is used then a closure filter will be assumed.
If a CODE reference is not used, a method filter will be assumed. In a method filter, the reference can be used to store context information. The reference will be blessed into the package by "filter_add".
See Filter::Util::Call for examples of using context information using both method filters and closure filters.