This is a rewrite of feature vectors in lnwire. This has a few
benefits:
1) a simpler interface
2) separate structs for a plain set of feature bits and a feature
vector with associated feature names
their respective feature sets
3) loosened requirements that bits MUST be assigned in pairs
4) fix endianness of encoding/decoding
This commit does away with all the old manual message equality tests
and replace it with a single property-based test that uses the
testing/quick package. This test uses a single scenario which MUST hold
for all the messages type and all possible messages generated for those
types. As a result we are able to do away with all the prior manually
generated test data as the fuzzer to scan the input space looking for a
message that violates the scenario.
'init' message is the first message reveals the features supported or required
by this node. Nodes wait for receipt of the other's features to simplify error
diagnosis where features are incompatible. This message will help negotioate the
the features which are supported by both sides.
