man: generate manpages from .org files

Generate the manpages from org-documents which makes it a bit easier to
keep them update to date since I find org-syntax easier than troff, and
we can use include files.

man/muhome.inc

@@ -0,0 +1,12 @@
+** --muhome
+use a non-default directory to store and read the database, write the logs, etc.
+By default, ~mu~ uses the XDG Base Directory Specification (e.g. on GNU/Linux this
+defaults to =~/.cache/mu= and =~/.config/mu=). Earlier versions of ~mu~ defaulted to
+=~/.mu=, which now requires =--muhome=~/.mu=.
+
+The environment variable ~MUHOME~ can be used as an alternative to ~--muhome~. The
+latter has precedence.
+
+# Local Variables:
+# mode: org
+# End: