Get core-rs ready to be used as part of an SDK

[ChrisSchinnerl]

• Make sure serializer and deserializer produce the same output as core for the following types
  • Implement Deserialize for Address, Hash256 and Currency #31
  • Implement Deserialize for PublicKey, Algorithm, UnlockConditions, SiacoinOutputID, SiacoinInputID, SiacoinOutput, SiacoinInput, SiafundOutput and SiafundInput #32
  • Fix FileContract and FileContractRevision serialization #33
  • Implement deserializie for storage proof #38
  • Deserialize transaction signatures #39
  • Implement Deserialize for transaction #42
• Change Algorithm to struct instead of enum #40
• Add test to verify v1 signatures can be created and verified  #43
• Transaction Builder #45