Did some reorganizing.

Did some reorganizing.

- Moved prepare.manpage.contents template out of general.xsl file
  and into other.xsl; general.xsl templates are now all templates
  that are called multiple times for each refentry, while
  templates in other.xsl are called only once per each refentry.

- Removed get.metadata template; refentry metadata gathering is
  now done by common/refentry.xsl in a way that is independent of
  the final output format; so the common/refentry.xsl templates
  can be called not just by manpages stylesheets, but by
  stylesheets for any other output format

- Added a write.man.file template. This is basically just a
  wrapper around the write.text.chunk template; it takes "name"
  and "section" params, assembles those into a filename, then
  passes that filename to write.text.chunk