* Add interface to read body bytes in binding
* Add BindingBody implementation for some binding
* Fix to use `BindBodyBytesKey` for key
* Revert "Fix to use `BindBodyBytesKey` for key"
This reverts commit 2c82901cea.
* Use private-like key for body bytes
* Add tests for BindingBody & ShouldBindBodyWith
* Add note for README
* Remove redundant space between sentences