Prepare v0.2 (#527)

* v0.2: nimble and changelog

* eth-precompiles: C/Rust for RipeMD160 and KZG Point precompile

* draft release notes v0.2.0

* update Rust packages

* update PLANNING.md

* mention Nim minimum version

* mention the CI changes

Prepare for first release 0.1.0 (#422)