Breaking changes:

- Parcel and SignedParcel and its related methods changed.
  - Parcel's nonce and fee are now nullable
  - The r, s, v fields of the SignedParcel are replaced with the sig field
- SDK optional argument changed.
- ChangeSharedState changed.
- AssetMintTransaction changed.
- AssetAgent is not exposed anymore.
- No rollup build

Integration tests passed with codechain@0.1.0 (0cbd78a08164fa02278b27aa1dbf134b54c4a0cb)