Add gem "wdm" for Windows platforms to gemfile

Tested for Windows 7-64 ruby 1.9.3p448 (2013-06-27) [i386-mingw32]
Added middleman-deploy. Fixes issue #4.
Merge pull request #19 from paperdigits/issue_4

Added middleman-deploy. Fixes issue #4.
Merge pull request #16 from karland/master

Add gem "wdm" for Windows platforms to gemfile