doc: fix doxygen-link.py by skipping invalid entries in libnl.dict

Newer versions of doxygen (on Fedora20) treat the documentation
slightly different so that the following entires end up in
libnl.dict:

    \=api/group__attr.html#ga769cc7bd882aab17c3740dd83329d7e6
    »·······»·······NLA_PUT=api/group__attr.html#ga769cc7bd882aab17c3740dd83329d7e6
    NLA_PUT=api/group__attr.html#ga769cc7bd882aab17c3740dd83329d7e6

Especially, replacing r'\' breaks the generated html documentation.
Extend doxygen-link.py to strip whitespaces from the name and
skip over r'\'.

Also, when replacing the words in the output file, match them
using word boundaries r'\b'.

Also, don't print an additional newline after each processed line.

Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Thomas Haller <thaller@redhat.com>