Add Reline as a fallback library for Readline

* 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.

test/reline/test_key_stroke.rb

@@ -0,0 +1,51 @@
+require_relative 'helper'
+
+class Reline::KeyStroke::Test < Reline::TestCase
+  using Module.new {
+    refine Array do
+      def as_s
+        map(&:chr).join
+      end
+    end
+  }
+
+  def test_input_to!
+    config = {
+      key_mapping: {
+        "a" => "xx",
+        "ab" => "y",
+        "abc" => "z",
+        "x" => "rr"
+      }
+    }
+    stroke = Reline::KeyStroke.new(config)
+    result = ("abzwabk".bytes).map { |char|
+      stroke.input_to!(char)&.then { |result|
+        "#{result.as_s}"
+      }
+    }
+    assert_equal(result, [nil, nil, "yz", "w", nil, nil, "yk"])
+  end
+
+  def test_input_to
+    config = {
+      key_mapping: {
+        "a" => "xx",
+        "ab" => "y",
+        "abc" => "z",
+        "x" => "rr"
+      }
+    }
+    stroke = Reline::KeyStroke.new(config)
+    assert_equal(stroke.input_to("a".bytes)&.as_s, nil)
+    assert_equal(stroke.input_to("ab".bytes)&.as_s, nil)
+    assert_equal(stroke.input_to("abc".bytes)&.as_s, "z")
+    assert_equal(stroke.input_to("abz".bytes)&.as_s, "yz")
+    assert_equal(stroke.input_to("abx".bytes)&.as_s, "yrr")
+    assert_equal(stroke.input_to("ac".bytes)&.as_s, "rrrrc")
+    assert_equal(stroke.input_to("aa".bytes)&.as_s, "rrrrrrrr")
+    assert_equal(stroke.input_to("x".bytes)&.as_s, "rr")
+    assert_equal(stroke.input_to("m".bytes)&.as_s, "m")
+    assert_equal(stroke.input_to("abzwabk".bytes)&.as_s, "yzwabk")
+  end
+end