Add "test runner" support for cross builds.
 "test runner" means target simulator like QEmu, GDB sim, and so on. Also "test runner" might be debug agents for real targets.
If you do not setup test_runner, Rake will work same as before.
Support $0 variable.
Merge pull request #1155 from monaka/pr-support-global-zero-variable

Support $0 variable.
Fix checking for heredoc in mirb
Merge pull request #1159 from h2so5/fix-mirb-heredoc

Fix checking for heredoc in mirb
Change mruby-random License to MIT

refs: http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/license.html
Merge pull request #1160 from matsumoto-r/change_mruby_random_license

Change mruby-random License to MIT
Merge pull request #1150 from monaka/pr-add-test-runner-support

Add "test runner" support for cross builds.