Context-Generic Programming Updates: v0.3.0 Release and New Chapters

[maybevoid]

I'm excited to announce the release of v0.3.0 of the `cgp` crate, along with several new chapters of the CGP Patterns book!

Check out the linked blog post for more details. I also include here a summary of updates in this release:

- New chapters for Context-Generic Programming Patterns

  - Associated Types

  - Error Handling

  - Field Accessors

- `cgp` v0.3.0 Crate Release

  - New `cgp_type!` Macro

  - New `#[cgp_auto_getter]` Macro

  - New `#[cgp_getter]` Macro

  - New `CanWrapError` Trait

  - New `cgp-error-anyhow` Crate

  - New `cgp-runtime` Crate