Canceled Alda::method_missing. Use meta-programming to define methods…

… instead. You can now use `include Alda` to import such commands.

Alda command line support now can have options as well as subcommand options:
  Alda.play {port: 1108}, code: "piano: c"
The module REPLSession became a REPL class, whose instance represents a REPL session. It is for starting multiple sessions at the same time.
Stopped using the command line `alda repl` in alda-rb REPL.
Fixed the bug of repetition:
  Score.new { c*2*3 }.to_s
  # before => "c*3"
  # after  => "c*6"

examples/clapping_music.rb

@@ -19,6 +19,6 @@
 
 	tempo! 172
 	midi_percussion_ o2 set_note_length 8
-	v1; s{ play }*(12*13)
+	v1; s{ play }*12*13
 	v2; 13.times { s{ play; pattern.rotate! }*12 }
 end.play