Mirror Sublime-HTMLPrettify Subprocess and Logging Fixes

* Explicitly pass `os.environ` to `subprocess.check_output()`. Fixes
  bug in which the subprocess failed to inherit the package's environment,
  so `PluginUtils`' checks could find the Node binary but the new
  process could not.
* Add `print_diagnostics` setting, allowing the user to suppress verbose
  logging of JSBeautify's configuration.
Merge pull request #85 from phyllisstein/master

Mirror Sublime-HTMLPrettify Subprocess and Logging Fixes