Ability to inline extraFields configuration. New @goExtraField directive.

[atzedus]

@goExtraField directive added for inline configuration.

Example of use:

type User
	@goExtraField(
		name: "Session"
		type: "github.com/author/mypkg.Session"
		description: "A Session used by this user"
		overrideTags: "xml:\"session\""
	)
	@goExtraField(name: "Activated", type: "bool") {
	id: ID
	name: String
}

The generated code would look like:

type User struct {
  ID   string
  Name string
  // A Session used by this user.
  Session   mypkg.Session `xml:"session"`
  Activated bool
}

This is more usefull raise then configuration in yaml, like:

models:
  User:
    extraFields:
      Session:
        description: "A Session used by this user"
        type: "github.com/author/mypkg.Session"
        overrideTags: 'xml:"session"'
      Activated:
        type: "bool"

because all the fields of the model are in front of your eyes.

I have:

• Added tests covering the bug / feature (see testing)
• Updated any relevant documentation (see docs)

[StevenACoffman]

Thanks! Nice improvement!