* Change use of #attr into #attr_reader and #attr_accessor...

...to keep up with Ruby API changes and avoid noisy warnings.

All Ruby implementations supporting Ruby language level 1.9 or later give a warning on every use of attr with boolean.

The attar method is not well documented.

attr_reader, attr_writer, and attr_accessor are the recommended methods to use.

It would be great if this change could be merged and released.