move check condition to outside in while block

Refactor tests in kernel.rb

use mrb_str_cat_lit() intead of mrb_str_cat

Add test for Kernel#instance_variable_defined?

Could you add me to AUTHORS?

Delete `!!Notice!!` intro paragraph from README

It's become misleading since the release of 1.0.0 and the launch of mruby.org.

revert 38e9ce21 and API changed; mrb_get_backtrace() -> renamed to mrb_exc_backtrace since this is a backtrace method implementation of Exception; mrb_get_backtrace_at() -> removed; mrb_get_backtrace() -> added to get backtrace in array (like caller)

Compile assert.rb once.

Use mrb_str_new_lit instead of mrb_str_new for C string literal

fix bug for get_valid_iv_sym

use mrb_intern_lit instead of mrb_intern_cstr for C string literals

add test for __LINE__ and __FILE__

Introduce mrb_str_cat_lit

Use mrb_str_new_lit instead of mrb_str_new for C string literals

When sub-string is used in the following way, it does not work well.

o = Object.new
o.instance_variable_set(:@a, 1)
o.instance_variable_defined?("@abc"[0,2]) #=> false (this should be true)

Specialize C++ compiler in clang toolchain.

Update README.md; The URL of the mruby home-page is accessible.

fix missing spaces.