Add new API mrb_intern_cstr(). This is for naming orthogonality. mrb_intern is also left for backward compatibility.

Add an internal function intern_c(). It reduces function call parameter. For maintainability and performance.

bugfix escape charactor for Regexp class

Fix indentation in keywords

Update Travis CI build to install gperf

Add gem version to build summary

add mrbgem: mruby-enum-ext and some methods.

Merge branch 'pr-add-new-api-mrb_true_or_false_value' of https://github.com/monaka/mruby into monaka-pr-add-new-api-mrb_true_or_false_value

Some optimizes to vm.c

implement %I %i literal