add macro ARY_SHARED_P
add test for Kernel#instance_variable_defined?
add macro ARY_SET_SHARED
add macro ARY_UNSET_SHARED
Delete `!!Notice!!` intro paragraph from README

It's become misleading since the release of 1.0.0 and the launch of mruby.org.
Merge pull request #1754 from pje/patch-1

Delete `!!Notice!!` intro paragraph from README
boot_defclass: super may be NULL
forget to break in the switch statement
Could you add me to AUTHORS?
Implement sprintf("%c") for UTF-8.

* sprintf("%c") is changed to accept a string for which String#size returns
  1, even if it is longer than one byte, and to convert a Fixnum via
  Fixnum#chr (possibly returning more than one byte).  Thus, if the UTF-8
  gem is in use, a character will be understood as a single UTF-8 character.

* The change to sprintf depends on the implementation of Fixnum#chr added
  to mrbgems/mruby-string-utf8/src/string.c.

This should work with any other gem that implements a multibyte encoding, as
long as it implements String#size and Fixnum#chr as appropriate.
Update the Fixnum#chr test for UTF-8.
Merge pull request #1755 from cubicdaiya/issues/add_to_me_authors

Could you add me to AUTHORS?
Merge pull request #1751 from cubicdaiya/issues/test_for_instance_variable_defined_question

Add test for Kernel#instance_variable_defined?
should not continue loop when ci = NULL
use mrb_str_cat_lit() intead of mrb_str_cat
Refactor tests in kernel.rb
move check condition to outside in while block
make mrb_str_dump a bit faster
add mruby-strip tool to strip irep's debug info
Merge pull request #1757 from cubicdaiya/issues/use_mrb_str_cat_lit

use mrb_str_cat_lit() intead of mrb_str_cat