Add hex string types

[cubismic]

output go test in ./primitives is

[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
true
false

[144 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
0x00000000000000000000000000000000
PASS
ok      github.com/CodeChain-io/codechain-rpc-go/primitives     0.005s

[majecty]

go ethereum is a very huge project.
Can't we import just the rlp package?

[cubismic]

I'm looking for importing only rlp package but it is hard to find.

I did
go get github.com/ethereum/go-ethereum/rlp
but go mod includes every go-ethereum...

[majecty]

OK. Let's fix it later.

[majecty]

I added issue #13.