Allow packages in window.Packages to return a .then-able

[mickmcgrath13]

Original issue in canjs canjs/canjs/issues/2706
Corresponding bit-docs-prettify issue: bit-docs/bit-docs-prettify/issues/5

Where we loop over the packages, look for a deferred (has .then) and wait for that to resolve before proceeding.

Something like:

function processPackages(packageIndex, callback){
  var i = packageIndex || 0,
    packageNames = Object.keys(window.PACKAGES),
    packageName, packageResult;

  if(i === packageNames.length){
    if(typeof callback === 'function'){
      callback();
    }
    return;
  }

  packageName = packageNames[i];
    if (typeof window.PACKAGES[packageName] === 'function') {
        packageResult = window.PACKAGES[packageName]();
        if(packageResult && packageResult.then){
          packageResult.then(function(){
            processPackages(i+1, callback);
          });
        }else{
          processPackages(i+1, callback);
        }
    }else{
      processPackages(i+1, callback);
    }
};

// go through every package and re-init
processPackages(0, function(){
  init();
  setDocTitle();
});