Add gembox which contains all default GEMs

mrbgems/default.gembox

+MRuby::GemBox.new do |conf|
+  # Use standard Kernel#sprintf method
+  conf.gem "#{root}/mrbgems/mruby-sprintf"
+
+  # Use standard print/puts/p
+  conf.gem "#{root}/mrbgems/mruby-print"
+
+  # Use standard Math module
+  conf.gem "#{root}/mrbgems/mruby-math"
+
+  # Use standard Time class
+  conf.gem "#{root}/mrbgems/mruby-time"
+
+  # Use standard Struct class
+  conf.gem "#{root}/mrbgems/mruby-struct"
+
+  # Use extensional Enumerable module
+  conf.gem "#{root}/mrbgems/mruby-enum-ext"
+
+  # Use extensional String class
+  conf.gem "#{root}/mrbgems/mruby-string-ext"
+
+  # Use extensional Numeric class
+  conf.gem "#{root}/mrbgems/mruby-numeric-ext"
+
+  # Use extensional Array class
+  conf.gem "#{root}/mrbgems/mruby-array-ext"
+
+  # Use extensional Hash class
+  conf.gem "#{root}/mrbgems/mruby-hash-ext"
+
+  # Use extensional Range class
+  conf.gem "#{root}/mrbgems/mruby-range-ext"
+
+  # Use extensional Proc class
+  conf.gem "#{root}/mrbgems/mruby-proc-ext"
+
+  # Use extensional Symbol class
+  conf.gem "#{root}/mrbgems/mruby-symbol-ext"
+
+  # Use Random class
+  conf.gem "#{root}/mrbgems/mruby-random"
+
+  # Generate mirb command
+  conf.gem "#{root}/mrbgems/mruby-bin-mirb"
+
+  # Generate mruby command
+  conf.gem "#{root}/mrbgems/mruby-bin-mruby"
+end