Release 2.0.0-RC1

[stephanfeb]

Version 2.x of the library is a major refactor and breaks backwards compatibility
with several previous library APIs.

• A new TransactionBuilder class for composing Transactions
• Removal of the old Builder interface which was directly attached to the Transaction class
• A complete re-implementation of the Script Interpreter
• The Sighash class now exposes the SigHash Pre-Image; useful when creating OP_PUSH_TX spending scripts.
• A new ScriptBuilder class to make it easy to create custom locking/unlocking scripts.
• Merged contributed code to have better Flutter Web support.

---

This discussion was created from the release Release 2.0.0-RC1.