Add etsyn-to-6forms.py

Picks 6 noun forms out of the Filosoft morph. synth. output format.
The 6 forms go to STDOUT. Parallel forms are separated by |.
If one of the forms is missing then an error is writted to STDERR.

TODO: generalize this to adjectives and verbs as well.

Input example:

aadlik //_S_ *, //
    aadlik //_S_ sg n, //
    aadlik+e //_S_ pl g, //
    aadlik+ega //_S_ pl kom, //
    aadlik+eks //_S_ pl tr, //
    aadlik+el //_S_ pl ad, //
    aadlik+ele //_S_ pl all, //
    aadlik+elt //_S_ pl abl, //
    aadlik+ena //_S_ pl es, //
    aadlik+eni //_S_ pl ter, //
    aadlik+es //_S_ pl in, //
    aadlik+esse //_S_ pl ill, //
    aadlik+est //_S_ pl el, //
    aadlik+eta //_S_ pl ab, //
    aadlikk+e //_S_ pl p, //
    aadlikku //_S_ adt, //
    aadlikku //_S_ sg p, //
    aadlikku+de //_S_ pl g, //
    ...

Output example:

aadlik, aadliku, aadlikku, aadlikusse|aadlikku, aadlike|aadlikkude, aadlikke|aadlikkusid