Remove deprecate warning on Windows 

HighLine is using the Win32API, but Win32API is obsolete.
(Win32API = DL Wrapper)
And, DL is deprecated after Ruby 2.0.0.

* case 1: use Ruby 2.0.0
  * `DL is deprecated, please use Fiddle`
* case 2: use Ruby 1.9.3
  * `Win32API is deprecated after Ruby 1.9.1; use dl directly instead`