Add support for custom tags

[mfelipe]

Would be nice to have the possibility to add other struct tags automatically from the schema, besides json, yaml and mapstructure.

For example, with https://github.com/brianvoe/gofakeit, we can generate random data for testing.

Here I'm picking $comment as the source of this metadata, but it's just an idea:

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "id": "https://example.com/case",
  "type": "object",
  "properties": {
    "url": {
      "type": "string",
      "$comment": "$go-jsonschema-tag:fake:\"{url}\"",
      "$comment": "Just a regular comment to be ignored..."
    },
    "id": {
      "type": "string",
      "$comment": "$go-jsonschema-tag:fake:\"{number:1,10}\""
    },
    "html": {
      "type": "string",
      "$comment": "$go-jsonschema-tag:fake:\"skip\""
    }
  }
}

It would generate something like this:

type Tags struct {
	// Html corresponds to the JSON schema field "html".
	Html *string `yaml:"html,omitempty" fake:"skip"`

	// Id corresponds to the JSON schema field "id".
	Id *string `yaml:"id,omitempty" fake:"{number:1,10}"`

	// Url corresponds to the JSON schema field "url".
	Url *string `yaml:"url,omitempty" fake:"{url}"`
}

[mfelipe]

I've made the change as I needed it for a personal project. It's basic and won't break anything as far as I could test.

I'm open to do changes to it, open an Pull Request, etc.

https://github.com/mfelipe/go-jsonschema