doc: fate: Move documentation from .txt to .texi

  The fate.txt file is ported to texinfo format. Therefore the
fate.txt is renamed to fate.texi. The contents of the already
existing fate.texi file are discarded.

  However there should be no loss of information. If you find
anything missing, please report.

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>