added PSON

new file:   ProcSet/PSON
new file:   t/PSON.t
docs and features and fixes, oh my!

Makefile:
- new target doc:
  - depends on target gx
  - creates man and wiki pages
- target test:
  - added -P as gx option to all tests
  - added test for PSON
- target install-gx:
  - ensure $(PREFIX)/bin exists
  - install all of ProcSet/* instead of specific files
- new target install-man:
  - $ensure (PREFIX)/share/man/man1 and $(PREFIX)/share/man/man3 exist
  - install man pages
- target install:
  - depends also on install-man
- target clean:
  - removes: bin/gx docs/man/man[13]/* docs/md/*/* docs/pod/*/* docs/wiki/ProcSet-*, and all files matching '*~'

ProcSet/Test:
- added test x_ck
- updated POD

ProcSet/gx_init:
- added sconcat, saconcat, say, and gx_version
- updated POD

README.md:
- removed Test Framework section
- added Included Libraries section

src/gx.c:
- updated usage()
- added option --gx_version
- added handling of gs's -c option

t/fizz.psx:
- added -P as gx option

new files:
- docs/WARNING: Files in subdirectories of this directory are auto-generated
- docs/gx.pod: gx(1) source
- docs/man/man1/gx.1
- docs/man/man3/PSON.3gx
- docs/man/man3/Test.3gx
- docs/man/man3/gx_init.3gx
- release_tools/gxpod2docs: creates docs