request for comments: introduce a regression test framework for bin/mruby and bin/mirb

in recent time, most bugs target on corner cases from `bin/mruby` and `bin/mrirb`, but we haven't any test on them yet. we already have a good _unit test_ framework in mruby language, but it's hard to cover corner cases for interpreter, and as it shows that sometimes it is hard to add regression tests for proven bugs, like #1563, #1572, and #1564. 

I think it would be better to introduce a test framework separately for the binaries as _integration test_, so we can collect regression tests easier. 

this PR introduced `roundup.sh` (which is also MIT license) as the test framework in bash, with some sample test cases, and enabled it in travis but disabled it by default in other cases, for it might not works on windows.

any comment or advice is appreciated

thank you