Filterx parse cef/leef #1

[bshifter]

Introduces the parse_cef and parse_leef functions to the filterx module.
Currently, parse_leef supports only LEEF version 1.0. Support for LEEF 2.0 will be included in a future update.

examples:

filterx {
   leef = parse_leef(leef_message);
   cef = parse_cef(cef_message);
}