Add comprehensive tests for Marshal and Encoder.
Add comprehensive tests for Marshal and Encoder.

rasky/go-xdr,dajohi/go-xdr,nullstyle/go-xdr,dajohi/go-xdr,postfix/go-xdr,rasky/go-xdr,davecgh/go-xdr,nullstyle/go-xdr,postfix/go-xdr,davecgh/go-xdr