Move over more parameter normalization

[Lucas Hrabovsky]

https://github.com/imlucas/version.mongodb.parts/blob/bb78c8ccd7533b7bb5b55d51431aae0ea2797fbd/lib/index.js#L19-L36

Some systems do weird things that would require extra logic in download scripts (eg '64bit' and 'Windows' in python). Make it easier for everyone so it just lives here.

req.locals = {
    opts: {
      branch: req.param('branch', 'master'),
      platform: req.param('platform', 'linux').toLowerCase(),
      bits: req.param('bits', '64').replace(/[^0-9]/g, ''),
      version: req.param('version'),
      debug: req.param('debug'),
      distro: req.param('distro')
    }
  };

  if(req.locals.opts.platform === 'darwin'){
    req.locals.opts.platform = 'osx';
  }
  if(req.locals.opts.platform === 'windows'){
    req.locals.opts.platform = 'win32';
  }