Add mrb_class_get_under()

Fix a few unsigned signed comparison warnings

Fix Range#==

Refactor range_eql() func in rangec.c and add Range#eql? method test.

Refactor mrb_range_eq() func in range.c.

Refactor mrb_obj_eq() func in object.c.

add nil.to_a, nil.to_f, nil.to_i methods

refactor mrb_realloc() in gc.c

crc.c - replace POSIX with C99 header

Refactor mrb_hash_empty_p() func in hash.c

ArgumentError raised when mrb_get_args(mrb, "z", ...) receives substring.

Fix include path of ArduinoDue example

Visual Studio 2013 support (and two other fixes)

Avoid read_escape() in case of regexp

remove the redundant codes with mrb_malloc_simple()

- VC12 has better C99 library support due to C++11
- defined strtof for VC11 or older
- define "inline" only if the C compiler is used

Refactor mrb_hash_has_keyWithKey() func in hash.c

Add arena save/restore around use of hash KEY.

Fix crash on load *mrb