[m-rev.] for review: add unboxed_readers to the stream module

[Julien Fischer]

Hi Dirk,

On Sat, 18 Apr 2020, Dirk Ziegemeyer wrote:

> maybe change naming of the new instance to stream.reader_unboxed to be consistent with
> io.read_char vs.
> io.read_char_unboxed

I considered that, however one of the other variant reader type classes
in the stream module is named bulk_reader, so I was trying to be
consistent with that.

I think read_char_unboxed should be changed to unboxed_read_char.

Julien.