Additional function to get property value as array.

Add asArray() function to split property values with given separator into multiple values in an array.
Expecting return as an array, I believe there is no need to have default value, and it might not fit into existing function, so I separated the function to keep any backward compatibility.

One note: this function strips white space around the words automatically, so if you have following property for example:

hostnames=boo, foo, woo

expected return value would be:

["boo", "foo", "woo"]