message: add FieldEntry constructor, closes
diff: @@ -23,6 +23,15 @@ pub struct FieldEntry {
  }
  impl FieldEntry {
  + /// Creates a new field entry given a name and a field type
  + pub fn new(field_name: String, field_type: FieldType) -> FieldEntry {
  + assert!(is_valid_field_name(&field_name));
  + FieldEntry {
  + name: field_name,
  + field_type,
  + }
  + }
  +
  /// Creates a new u64 field entry in the schema, given
  /// a name, and some options.
  pub fn new_text(field_name: String, text_options: TextOptions) -> FieldEntry {
  