Refactor Reline::Core (#561)

* Use Reline::Core.encoding instead of directly referencing IOGate

* Set input/output based on the IOGate's interface

lib/reline.rb

@@ -91,36 +91,36 @@ def completion_append_character=(val)
       if val.nil?
         @completion_append_character = nil
       elsif val.size == 1
-        @completion_append_character = val.encode(Reline::IOGate.encoding)
+        @completion_append_character = val.encode(encoding)
       elsif val.size > 1
-        @completion_append_character = val[0].encode(Reline::IOGate.encoding)
+        @completion_append_character = val[0].encode(encoding)
       else
         @completion_append_character = nil
       end
     end
 
     def basic_word_break_characters=(v)
-      @basic_word_break_characters = v.encode(Reline::IOGate.encoding)
+      @basic_word_break_characters = v.encode(encoding)
     end
 
     def completer_word_break_characters=(v)
-      @completer_word_break_characters = v.encode(Reline::IOGate.encoding)
+      @completer_word_break_characters = v.encode(encoding)
     end
 
     def basic_quote_characters=(v)
-      @basic_quote_characters = v.encode(Reline::IOGate.encoding)
+      @basic_quote_characters = v.encode(encoding)
     end
 
     def completer_quote_characters=(v)
-      @completer_quote_characters = v.encode(Reline::IOGate.encoding)
+      @completer_quote_characters = v.encode(encoding)
     end
 
     def filename_quote_characters=(v)
-      @filename_quote_characters = v.encode(Reline::IOGate.encoding)
+      @filename_quote_characters = v.encode(encoding)
     end
 
     def special_prefixes=(v)
-      @special_prefixes = v.encode(Reline::IOGate.encoding)
+      @special_prefixes = v.encode(encoding)
     end
 
     def completion_case_fold=(v)
@@ -181,20 +181,16 @@ def dialog_proc(name_sym)
 
     def input=(val)
       raise TypeError unless val.respond_to?(:getc) or val.nil?
-      if val.respond_to?(:getc)
-        if defined?(Reline::ANSI) and Reline::IOGate == Reline::ANSI
-          Reline::ANSI.input = val
-        elsif Reline::IOGate == Reline::GeneralIO
-          Reline::GeneralIO.input = val
-        end
+      if val.respond_to?(:getc) && Reline::IOGate.respond_to?(:input=)
+        Reline::IOGate.input = val
       end
     end
 
     def output=(val)
       raise TypeError unless val.respond_to?(:write) or val.nil?
       @output = val
-      if defined?(Reline::ANSI) and Reline::IOGate == Reline::ANSI
-        Reline::ANSI.output = val
+      if Reline::IOGate.respond_to?(:output=)
+        Reline::IOGate.output = val
       end
     end
 
@@ -313,7 +309,7 @@ def readline(prompt = '', add_hist = false)
       otio = Reline::IOGate.prep
 
       may_req_ambiguous_char_width
-      line_editor.reset(prompt, encoding: Reline::IOGate.encoding)
+      line_editor.reset(prompt, encoding: encoding)
       if multiline
         line_editor.multiline_on
         if block_given?
@@ -565,7 +561,7 @@ def self.core
     @core ||= Core.new { |core|
       core.config = Reline::Config.new
       core.key_stroke = Reline::KeyStroke.new(core.config)
-      core.line_editor = Reline::LineEditor.new(core.config, Reline::IOGate.encoding)
+      core.line_editor = Reline::LineEditor.new(core.config, core.encoding)
 
       core.basic_word_break_characters = " \t\n`><=;|&{("
       core.completer_word_break_characters = " \t\n`><=;|&{("