__contains__ method for concatenated code

[David Lucas]

For now, __contains__ is not implemented for concatenated codes. So c in C (with c a codeword, and C a concatenated code) relies on default implementation which uses the generator matrix... Which does not exists (for now) in concatenated codes!

[David Lucas]

Implemented unencode method for EncoderConcatenatedCodeOuterField. Known issue : does not work if called by code.unencode(word) (see issue #98)

→ <<cset 68c07e8a95f5>>

[David Lucas]

Now ConcatenatedCode.generator_matrix exists.

[Johan Rosenkilde]

We keep thinking of concatenated codes being huge and would like to avoid building the generator matrix except if the user really asks for it. Membership of a concatenated code can be decided by membership of the constituent codes. If unencode was written in the right way, __contains__ could just call this function, and if unencode did not throw an exception, it returns True.