GRS Gao decoder's implimit message space is currently polynomials

[Johan Rosenkilde]

Two possibilities:

• Either this is changed into being a vector (and the Gao decoder's connected_encoder is the EvaluationVector encoder)
• Or current behaviour is kept and the connected encoder is EvaluationPolynomial (which is yet to be written, see #42)

[David Lucas]

Current behaviour was kept, so connected_encoder is now polynomial