mrdb: minor changes

remove unnecessary _WIN32 preprocessor check

SIZE_MAX < UINT32_MAX is false on Win32 / Win64.

Fix String#slice! raise TypeError or return invalid value.

use mrb_str_xxx_lit for mrdb.

mrdb: fix heap-use-after-free

clang 3.5.0 with -Wextra produces a -Wignored-qualifiers diagnostic.

C99+TC3, 7.19.7.1p2: [...] the fgetc function obtains that character as
an unsigned char converted to an int [...]

Fix an error when calling a method implemented in C by super() with argu...

[ci skip] run spell checker on doc/debugger/README.md and fixed typos mentioned from @bovi and @rmosolgo; ref #2640

Fix an error when calling a method implemented in C by super() with arguments. This fix makes the following code workable:

Expected:

class MRBTime < Time; def self.new; super(2012, 4, 21); end; end
MRBTime.new # => Sat Apr 21 00:00:00 2012

Actual:

class MRBTime < Time; def self.new; super(2012, 4, 21); end; end
MRBTime.new # => can't convert nil into Integer (TypeError)

mruby-1.1.0

Fix mailing list description; ref #2635

fix mrb_notimplement typo

Implement C API mrb_notimplement

Fix mrb_iv_check function decleration

Modify Arduino build config for IDE >= 1.5.7

%zu format is not supported by MSVC

Arduino IDE >= 1.5.7 Changed ARDUINO_PATH from `Contents/Resources/Java` to `Contents/Java`, mentioned in #2632