Add include method for POD documentation

Add include method for POD documentation

Add a preprocessor for POD documentation that handles a custom
=include directive.  Demonstrate how to use the preprocessor by
factoring out all the standard PTS options into a separate POD
fragment and including that fragment in all the PTS commands that
take the standard options instead of including that documentation
in each separate file.

Change-Id: If5255efc6d3fc670b38a9898b3d7d3c60af04fcf
Reviewed-on: http://gerrit.openafs.org/2440
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>