IRB uses Reline's 3 dynamic real-time callbacks with calling Ripper;
output_modifier_proc, prompt_proc, and auto_indent_proc. These processing
times make the paste time too long.
https://github.com/ruby/reline/commit/beec3399a8
The command prompt on Windows always uses Unicode to take input and print
output but most Reline implementation depends on Encoding.default_external.
This commit introduces an abstracted structure about the encoding of Reline.
