adding code to allow for responsive size mapping & refresh

Where I work, we have found this project very helpful & reliable. Recently responsive ads were added as a requirement. To accomplish this, I needed to patch the code so size mapping could be passed to each ad slot before load. We found the mapping works before init & after refresh.
Which brings me to the $.dfpRefresh(); method. This obviously can be called at any time and can be used for more than just responsive ads. Hope this code is found to be useful. Cheers! -Daniel