* lib/reine.rb, lib/reline/*: Reline is a readline stdlib compatible
  library.
* lib/readline.rb: Readline uses a fallback to Reline when ext/readline
  doesn't exist.
* tool/sync_default_gems.rb: add ruby/reline as a default gem.
* appveyor.yml: add "set RELINE_TEST_ENCODING=Windows-31J" for test suit
  of Reline, and add "--exclude readline" to "nmake test-all" on Visual
  Studio builds because of strange behavior.
* spec/ruby/library/readline/spec_helper.rb: skip Reline as with
  RbReadline.