Avoid read_escape() in case of regexp
Visual Studio 2013 support + strtof + inline

- 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
Fix include path of ArduinoDue example
include inttypes.h if _MSC_VER is not defined
fix unnecessary exception in mrb_get_args with "z" format.
Refactor mrb_hash_empty_p() func in hash.c
replaced POSIX header with standard C header
Merge pull request #1310 from iij/pr-fix-regexp-escape

Avoid read_escape() in case of regexp
Merge pull request #1311 from cremno/msvc-2013-support

Visual Studio 2013 support (and two other fixes)
Merge pull request #1312 from kyab/fix_due_example

Fix include path of ArduinoDue example
Merge pull request #1313 from mimaki/fix-mrb_get_args-z-format

ArgumentError raised when mrb_get_args(mrb, "z", ...) receives substring.
Merge pull request #1314 from suzukaze/refactor-hash-c

Refactor mrb_hash_empty_p() func in hash.c
Merge pull request #1317 from cremno/crc.c-include-stddef.h

crc.c - replace POSIX with C99 header