Use direct implementation on u8/char to implement AsciiExt
Use direct implementation on u8/char to implement AsciiExt

The methods were copied to u8/char, so we can just use it in
AsciiExt impls to avoid duplicate code.

GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust