Added initial support for file type reports

Added initial support for file type reports

It may distinguish between code, documentation, translations, etc.
Hence, it provides the basic feature to get more accurate reports.

It does not replace the current stats, it is only add the
possibility to generate reports by file type.

This feature was implemented originally by Gregorio Robles in
CVSAnalY http://tools.libresoft.es/cvsanaly/  Gregorio agreed to
add his code here.

Signed-off-by: Germán Póo-Caamaño <gpoo@gnome.org>