Translated German comments in filerec.hxx and doxygen-ify.

Moved general file format description to be included in
class SfxMiniRecordReader documentation.
Changed '@example' to @par Example @code ... @endcode,
since Doxygen interprets @example as "all this file is an example",
which is not what was meant.

Change-Id: I01a91e7f1166b37dcb4e20368b4f70a908b4576b
Reviewed-on: https://gerrit.libreoffice.org/9957
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>