* Move man_docs and md_docs into new doc pkg
* Replace *bytes.Buffer with io.Writer
* Replace c == cmd.helpCommand with c.IsHelpCommand()
* Remove redundant len(children) == 0 check in HasSeeAlso
* Duplicate test setup for doc generation
We previously had this weak argument called projectName which let you
set a single part of a man page header. Instead do the best we can if
the caller doesn't pass us anything, but let the caller specify anything
they want.
