This module is provides the interface to allow the creation of Source
Filters which use a Unix coprocess.
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.
The function, filter_add installs a filter. It takes one
parameter which should be a reference. The kind of reference used will
dictate which of the two filter types will be used.
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
See Filter::Util::Call for examples of using context information
using both method filters and closure filters.