Windows fixes: Setting environment variables in command line; Redirecting to null device

* On Windows platforms, calls to Kernel#system issues commands to Windows Command Interpreter (cmd.exe). Windows Command Interpreter does not support setting of environment variables at the beginning of a command. This pull request moves the setting of environment variables inside the command string passed to sh where environment variables are processed as expected.

* Replace use of '/dev/null' with Guard::DEV_NULL, a constant that is evaluated at load time Guard is loaded (see guard/guard#365). The constant is set 'NUL' on Windows to '/dev/null' on other platforms.
Merge pull request #8 from cablegram/windows-fixes

Windows fixes: Environment variables in command line; Redirecting to null device
Version bump to 0.4.4
update rake tasks
Use two parameter form of #system to avoid setting environment variables on the command line

* Partially reverts d02a01711c9b4e8fb5e402fc832d29bcc7a95e02
* Avoids setting environment variables as a command prefix which is not supported by the Windows command processor
Use Process.kill instead of system("kill...")

* The version of kill.exe (v 1.14 cygwin) distributed with git for windows (v 1.8.1.msysgit.1) fails on Windows. Using Process.kill works fine.
Merge pull request #10 from cablegram/windows-fix-kill-process

Use Process.kill instead of system("kill...")
Merge pull request #9 from cablegram/windows-fix-setting-env-vars

Use two parameter form of #system to avoid setting environment variables...
deprecated 1.8.7
Version bump to 0.4.5
Use the correct option name in initialization: s/:force_runs/:force_run/

Referenced as :force_runs only in this one place. Referenced as :force_run in three places:
  ./lib/guard/rails/runner.rb:15
  ./README.md:37
  ./spec/lib/guard/rails/runner_spec.rb:210

No functionality changes as a result of this fix. Just a typo fix/clean up.
Merge pull request #11 from cablegram/fix-typo-force-runs

Use the correct option name in initialization: s/:force_runs/:force_run/
Version bump to 0.4.6