Add update to CMake files to provide documentation build and install targets for manpages.

[jolly-fellow]

• Move the script generating the man page to cmake

Decision: do we remove the ROFF formatted generated man page? If so, we may need to update readme to instruct how to generate this.

• After this decision, we may wish to replicate this issue across relevant repos (DUNE, CDT)

[stephenpdeos]

Blocked by #32

Related to https://github.com/AntelopeIO/cdt/issues/134, https://github.com/AntelopeIO/DUNE/issues/143