Add optional params to toolchain configuration

Add how to use  mrb_gc_arena_save()/mrb_gc_arena_restore() doc

Add regression test for #2933

Migrating from legacy to container-based infrastructure.
http://docs.travis-ci.com/user/migrating-from-legacy/

Add gem test dependencies

Distribute MRuby's source as a Ruby gem

Refator Hash#fetch test

LinkerConfig is a struct with five params

chop with utf-8. fix #2967

support Regexp literal option: //n and //u

fix tests on windows.

'bin/mruby' not work on windows. so correct command name and quoted arguments.

Small Markdown updates to README.md

Small copy and styling updates

fix signature of mrb_class_new_instance()

fix String#inspect with MRB_UTF8_STRING

dd925578 changed the order of arguments,
but it doesn't seem intentional.

cf. #2963