add unicode support facilities

[cthulhu-irl]

Description

The Stream is only about ascii and bytes right now, and it's hard to get utf code points. For example when validating json's quoted string, we have to manually handle utf code points.

It would save a lot of time to have facilities to support unicode comparisons and getting/validating code points.

Goals

• supporting common character encodings to cover variety of use cases and user base.

Definition of Done

• unspecified