Geocode large number of addresses using google map authentication for the standard API.
Geocode function in ggmap Package R doesn't have an option to input API key for standard plan. 'geocodeAPI.R' file modified those function such that we will able to use API key when trying to geocode address. Geocoding address code is modified from shannelynn work http://www.shanelynn.ie/massive-geocoding-with-r-and-google-maps/