fix ISO reference number of String#=~.
add operator "!~".
Merge pull request #1653 from iij/pr-fix-iso-ref-string-match

fix ISO reference number of String#=~.
Merge pull request #1654 from iij/pr-not-match-operator

add operator "!~".
Added rewrite of Array#[] to mruby-array-ext gem, so that arrays can be sliced
with Ranges (as a[1..-2])
String#length should be an alias of String#size
Merge pull request #1656 from h2so5/string-length-utf8

String#length should be an alias of String#size
Merge pull request #1655 from pbosetti/master

Added rewrite of Array#[] to mruby-array-ext gem
hash value of enumerable should be obtained from its elements; close #1658
hash value of enumerable should be obtained from its elements; close #1658
Merge branch 'master' of github.com:mruby/mruby
Increase test coverage of mruby-struct
Merge pull request #1659 from carsonmcdonald/threestructtests

Increase test coverage of mruby-struct
describe call stack overwritten problem of mrb_get_backtrace; close #1661
escape non-ascii characters correctly in String#inspect
Merge pull request #1662 from h2so5/fix-string-inspect

escape non-ascii characters correctly in String#inspect
fix utf-8 codepage
Merge pull request #1663 from h2so5/fix-utf8-codepage

fix utf8 codepage
add enable_debug to build_config.rb
add callback invocation from OP_DEBUG