Add support for Generics to Huddle.

[nc6]

We allow Haskell functions to be used as generic
rules by implementing the binding function.

Currently this is only implemented for one or two
generic parameters, but conceptually supports any
number.

Examples are provided both in the Conway.hs file
and in the tests. The generated CDDL for Conway
now looks like:

transaction_body = {0 : set<transaction_index>
                    , 1 : [* transaction_output]
                    , 2 : coin
                    , ? 3 : uint
                    , ? 4 : certificates
                    , ? 5 : withdrawals
                    , ? 7 : auxiliary_data_hash
                    , ? 8 : uint
                    , ? 9 : mint
                    , ? 11 : script_data_hash
                    , ? 13 : nonempty_set<transaction_input>
                    , ? 14 : required_signers
                    , ? 15 : network_id
                    , ? 16 : transaction_output
                    , ? 17 : coin
                    , ? 18 : nonempty_set<transaction_input>
                    , ? 19 : voting_procedures
                    , ? 20 : proposal_procedures
                    , ? 21 : coin
                    , ? 22 : positive_coin}

...

constr<a0> = #6.1([* a0])
              / #6.2([* a0])
              / #6.3([* a0])
              / #6.4([* a0])
              / #6.5([* a0])
              / #6.6([* a0])
              / #6.7([* a0])
              / #6.2([uint, [* a0]])

nonempty_set<a0> = set<a0>

set<a0> = [* a0]

[nc6]

@lehins FYI

[lehins]

LGTM.