clean -Wunused-function when defined DISABLE_STDIO

Add a Test Case for #359 Array Corruption

Add ary_modify to prevent corrupting shared array.

Could you add me to AUTHORS?

Replace Tab with spaces in src/parse.y

Use mrb_calloc if you want zero cleard buffers.

Add tests for Modules

Improvement of Module#include.

Optimize range check.

Brush up mrb_calloc().

- Add some methods: append_features, included_methods and included.
- Modify Module#include to call append_features and included.