constructor (schema, schemaRefs) {
    this.schema = schema
    this.schemaRefs = schemaRefs || {}
    this.suggestions = {}
    this.suggestionsRefs = {}
    this._buildSuggestions()
  }
SchemaTextCompleter class implements the ace ext-language_tools completer API,
and suggests completions for the text editor that are relative
to the cursor position and the json schema