folder([folderPath])
Returns a folder object. Note that the resulting folder object can either refer to an already existing folder or if the folder does not exist, it can create a preliminary “virtual” folder that refers to a folder that could be created later.
Type: function
Parameter(s):
- folderPath {String} Optional:The path of the folder. 
Returns:
- 
    {Folder}:
 Folder at the given path. If no path is given, but the document is already saved, the document’s data folder will be returned. 
Example(s):
Get a folder from the desktop and load its files
var myImageFolder = folder("~/Desktop/myImages/");
var myImageFiles = files(myImageFolder);
Get the data folder, if the document is already saved
var myDataFolder = folder();