code: function addSchemaField(schema, pathName, fieldSpec) {
  	const fieldSchema = {};
  	fieldSchema[pathName] = fieldSpec;
  	return schema.add(fieldSchema);
  }
docs: Adds a field/path to the given schema
  @param {Schema} schema mongoose-schema to add the fields to
  @param {string} pathName name of the path to add
  @param {object} fieldSpec specification of the field to add
  @returns {*} The updated schema