Fixed irep index overflows, when defining new closure.

Issue #1137.
In the present implementation, when calling mrb_load_string continuously, irep is not released.
Therefore, a 16-bit index was overflowing.
Merge pull request #1175 from kurodash/pr-irep-idx-overflow

Fixed irep index overflows, when defining new closure.
Add mruby-range-ext
Merge pull request #1178 from h2so5/mruby-range-ext

Add mruby-range-ext
Add closing double-quotes
Fix "implementaion" to "implementation"
Add Visual Studio 2010 subsection to Toolchains section of README.md

To follow h2so5/add-vs2010-toolchain
Update doc/compile/README.md about mruby and mirb
Merge pull request #1179 from carsonmcdonald/mrubyhtypofix

Fix "implementaion" to "implementation"
Merge pull request #1181 from trmmy/follow_readme_adding_vs2010.rake

Add "Visual Studio 2010" subsection to "Toolchains" section of doc/compile/README.md
Merge pull request #1180 from trmmy/typo

Add closing double-quotes to doc/compile/README.md
Merge pull request #1182 from trmmy/move_tools

Update doc/compile/README.md about mruby and mirb
Add Proc#arity
Merge pull request #1183 from h2so5/proc-arity

Add Proc#arity
rollback stack before executing ensure clause.
catching NameError here is not desirable.
Minor code format changes.
Fix typo.
Merge pull request #1184 from iij/pr-ensure-on-correct-stack

Rollback stack before executing ensure clause.
Merge pull request #1186 from carsonmcdonald/mrbcfixup

Minor format changes and a typo fix