Meta schema

[brettz9]

feat: add meta schema

Has the following advantages:

1. Convey the syntax to learners of Zodex JSON
2. Sanity check our own test schemas and user schemas
3. Facilitate the building of a UI to input an arbitrary Zodex JSON schema

Also:

• Make object's properties optional
• Add symbol to SzKey

[brettz9]

Realized I had my status set to Busy for a while, but I'm actually available now if you're able to review... :-)

[Gregoor]

Funky idea! Two comments:

1. I'd rename it to schema.zodex.json so that all kinds of tooling works by default (mainly thinking about editors and syntax highlighting)
2. I'd prefer not to make properties optional. I prefer things only to be in expressible in as many ways as necessary (in this case, an empty object). Or is it necessary?

[brettz9]

1. I'd rename it to schema.zodex.json so that all kinds of tooling works by default (mainly thinking about editors and syntax highlighting)

Sure, done.

2. I'd prefer not to make properties optional. I prefer things only to be in expressible in as many ways as necessary (in this case, an empty object). Or is it necessary?

No, it's not necessary. The idea was just to make it easier if hand-crafting the JSON, but that's fine. Changed back.

[brettz9]

The large block in the testing file was moved and also changed to complete test coverage.