rewrite manpages in mdoc(7)

[janstary]

Currently, the manpages u2ps(1) and psfrem(1)
are written in the traditional man(7) markup language.
I am proposing to rewrite them into the semantic markup
of the mdoc(7) language. I am willing to do the work.

Both the man(7) and mdoc(7) languages have been around for decades,
and are supported by the prevalent formatters: groff(1) on most Linuxes
and mandoc(1) on the *BSDs and some others. In particular,
there is nothing to install or reconfigure on most systems

• both formats can be rendered with man(1)
  or processed into plaintext, html, pdf, or ps.

The main point is that mdoc(7) allows for constructs like

    .Op Fl f Ar arg

meaning

    there is an optional 'f' flag
    which takes an 'arg' argument

as opposed to

    switch to italics, type a bracket, a dash, "f",
    then switch to boldface and type "arg"

in the physical roff markup of man(7).

Similarly for other constructs like cross-references,
filenames, author emails, env variables, etc.

As an example, here is a rewrite of psfrem.1; while here,

• spell the [options] out explicitly
• fix "-d var" vs "-d name"
• slight reformulations