[Groff] Adding section number to man-page, e.g. groff.1.man and groff.7.man for groff.man

[Bernd Warken]

The naming of all man-pages in the groff source tree is quite chaotic.

Only <page>.man is used, information of the section is available only in the
Makefile of the directory.

Then these man-pages are transferred to <page>.n using `.man.n:` in
main `Makefile.am` on the top of the source tree.

Then each generated <page>.n-files are moved to <page>.[157].

### new concept

1) To improve the total handling, I propose to use a starting man-page
`<page>.[157].man' instead of <page>.man.

2) This will be transported with the usual `.man.n:' into `<page>.[157].n'.

3)  Modifying a part of the top Makefile.am, the `.n' is removed and the file
is installated as `<page>.[157]'.

### old-fashion concept

A similar concept with `<page>.[157]n' was proposed and discussed in october
2014.  As this concept is not as suitable, I do not propose this old proposal 
again.

Bernd Warken