Add support for missing settings and change the allowedChildren to allowedBlocks

[ingeniumed]

Description

• Add support for settings that didn't work before. This includes typography, color.gradients, spacing, etc. Only duotone is left and that's been documented in the limitations. For the MVP, that's fine as it's proving to be tricky to resolve.
• Add more examples to show how the missing properties would work.
• Switch allowedChildren to allowedBlocks, and upgrade the version from 0.1.0 to 0.2.0 to account for this. Thanks @alecgeatches for pointing this out in the previous PR.
• Re-order the README to make the flow better for new plugin users.

Note: While this is a breaking change, given we are in beta its fine. We don't need to add support for backward versions that are a part of the beta.

Fixes #22
Fixes #23

Steps to Test

• Run the tests
• Use the new example in your governance-rules.json and ensure that everything works as expected.

[alecgeatches]

🔥 This works great! The governance rules could handle every setting I tried to throw at them.

While testing I noticed some allowedBlocks behavior and related issues with the core/list block documented in #30. However, I don't think those are related to the changes here.

Great job figuring this out!

[ingeniumed]

Fixes #26