v2.0.0-alpha.1

This release brings two exciting updates! First, contracts can now be built using the
stable Rust toolchain! Don't ask us how we managed to do this 👻.

Secondly, it allows you to build ink! v4.0.0-alpha.1, which introduced a small - but
breaking - change to the ink! ABI as part of paritytech/ink#1313.

Added

• Add support for ink!'s version metadata field - #641

Changed

• Build contracts and dylint driver with stable - #698
• Compile dylints when compiling the contract - #703
• Move transcode example to doc test, add helper method - #705
  • Note that alongside this PR we released [email protected]
• Replace custom RPCs by state_call - #701

Fixed

• Fix tracing_subscriber filtering - #702