Module no_std_io

Available on doc or test only.

no_std_io modifications

(↑) This module includes derived work from the no_std_io crate (a fork of the core2 crate), including the following modifications:

• removed memchr dependency.
• prefix items with Io and io_.
• add new items: IoEmpty, IoRepeat.
• replace not very sound implementations using Initializer with safer ones.
• add safe and unsafe internal implementations of previously only unsafe ones.
• replaced extensive documentation copied from std by links to original docs.
• remove impls and conversions of recreated types for the replaced std types.