Add Draft 07 support (#50)

Add draft7 support, separate dependecies field, separate id behavior into id and anchor,  ignore other properties of ref objects.

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Co-authored-by: Jim Clark <slimslenderslacks@gmail.com>

Author: baptmont

jsonschema/doc.go

@@ -6,8 +6,8 @@
 Package jsonschema is an implementation of the [JSON Schema specification],
 a JSON-based format for describing the structure of JSON data.
 The package can be used to read schemas for code generation, and to validate
-data using the draft 2020-12 specification. Validation with other drafts
-or custom meta-schemas is not supported.
+data using the draft 2020-12 and draft-07 specifications. Validation with
+other drafts or custom meta-schemas is not supported.
 
 Construct a [Schema] as you would any Go struct (for example, by writing
 a struct literal), or unmarshal a JSON schema into a [Schema] in the usual