Add support for os specific feature detection

Similar to how we have ruby feature detection this ports the `windows?` method from core and adds a method for detecting windows file paths (a sort of follow up to #108), idea would be to replace the usage of `world.windows?` with this and refactor #108 
For the specific problem I'm looking at now would File::ALT_SEPARATOR be a
better way to check if we need to use a the alternate path logic?

On Monday, September 8, 2014, Jon Rowe <notifications@github.com> wrote:

> In lib/rspec/support/os.rb:
>
> > @@ -0,0 +1,19 @@
> > +module RSpec
> > +  module Support
> > +    # @api private
> > +    #
> > +    # Provides query methods for different OS or OS features.
> > +    module OS
> > +      def windows?
> > +        RbConfig::CONFIG['host_os'] =~ /cygwin|mswin|mingw|bccwin|wince|emx/
> > +      end
> > +      module_function :windows?
> > +
> > +      def windows_file_path?
> > +        RbConfig::CONFIG['host_os'] =~ /mswin|mingw/
> > +      end
>
> This is from #108 <https://github.com/rspec/rspec-support/pull/108>,
> @scarcher2 <https://github.com/scarcher2> indicated that windows file
> paths weren't used on cygwin as it's a "unix" like environment on windows.
> FWIW I believe:
>
>    - cygwin - Cygwin https://www.cygwin.com/
>    - mswin - Desktop Windows
>    - mingw - MinGW http://www.mingw.org/
>    - bccwin - Bordland C compiler
>    - wince - Windows CE
>    - emx - No idea.
>
> It makes sense to me that probably bccwin, wince, and emx be added to the
> file_path? regexp.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/rspec/rspec-support/pull/110/files#r17273157>.
>