Merge pull request #2418 from take-cheeze/sym_intern

Add `Symbol#intern`.

mrbgems/mruby-symbol-ext/mrblib/symbol.rb

@@ -1,6 +1,8 @@
 class Symbol
   include Comparable
 
+  alias intern to_sym
+
   def to_proc
     ->(obj,*args,&block) do
       obj.__send__(self, *args, &block)

mrbgems/mruby-symbol-ext/test/symbol.rb

@@ -42,3 +42,7 @@ end
 assert("Symbol#empty?") do
   assert_true :''.empty?
 end
+
+assert('Symbol#intern') do
+  assert_equal :test, :test.intern
+end