[Groff] groff index generation (for mom)

[Johann Höchtl]

Dear Groffers,

under
https://github.com/the42/makeindex

you will find a TeX-independed makeindex, announced here and now updated 
to upstream:
http://lists.gnu.org/archive/html/groff/2012-09/msg00065.html

Using Denis Wilsons wonderful indexing support for markup,
http://www.oxytropis.plus.com/groff/
http://lists.gnu.org/archive/html/groff/2012-09/msg00070.html

I tried to achieve the same for MOM. The result is here:
https://github.com/the42/makeindex/tree/master/troff/mom

The solution works,
https://github.com/the42/makeindex/blob/master/troff/mom/mom-pdf.mom.pdf?raw=true
but has the issue, that the index entry 'unequal' references physical 
page 7, while it should reference logical page 5 (section 6.3,  "... 
possible to create documents with unequal-sized pages.")

Questions:

* Is there a way to get the list of TMAC-directories?
https://github.com/the42/makeindex/blob/9323f810b38196f98ad379c304fc21c1fbc998a8/troff/mom/index.tmac#L19

And mom-specific:
* Does MOM have a macro for page break (or is .bp save?) and a way to 
set text in two columns with automatic overflow, when the main text is 
set single-column?


PS:
* I would be happy if someone is interested to tidy up makeindex 
(especially the Makefile) which is crude but working. See

* This is a hint, that mom with out-of-the-box index-support would be 
great ;)

Greetings,

   Johann