Add support to generate man pages in txt and md

Manual pages can now be generated in plain ASCII text as
well as in markdown. This is in addition to the prviously
generated postscript, troff and rst.  All output types are
generated when the build doc CMake configuration variable
is set high.

Signed-off-by: E. Scott Daniels <daniels@research.att.com>
Change-Id: Ib98e6df65c32944807a99a6c5b80859182038c4d
Signed-off-by: E. Scott Daniels <daniels@research.att.com>
40 files changed