(https://github.com/ruby/stringio/pull/201)

https://github.com/ruby/stringio/commit/26d8f60053

https://github.com/ruby/stringio/commit/d4b27b8681

(https://github.com/ruby/stringio/pull/197)

Previous doc merely linked to `IO#read`; new doc stays local, shows
examples using `StringIO`.

https://github.com/ruby/stringio/commit/e8b66f8cdd

(https://github.com/ruby/stringio/pull/196)

Previous doc merely linked to `IO#putc`. The new doc stays local,
provides examples using `StringIO` objects.

https://github.com/ruby/stringio/commit/8983f32c50

(https://github.com/ruby/stringio/pull/195)

Previous doc unhelpfully pointed to `IO#pread`; this PR documents
locally, with StringIO examples.

https://github.com/ruby/stringio/commit/806f3d9741

(https://github.com/ruby/stringio/pull/171)

https://github.com/ruby/stringio/commit/95a111017a

(https://github.com/ruby/stringio/pull/165)

Adds to "Position":  pos inside a character.

Makes a couple of minor corrections.

---------

https://github.com/ruby/stringio/commit/ff332abafa

Co-authored-by: Sutou Kouhei <kou@cozmixng.org>

(https://github.com/ruby/stringio/pull/190)

https://github.com/ruby/stringio/commit/77209fac20

(https://github.com/ruby/stringio/pull/188)

https://github.com/ruby/stringio/commit/66360ee5f1

https://github.com/ruby/stringio/commit/e2d24ae8d7