Get the archived version of a page closest to a particular date

Works with AWA, NZWA, IA, & UKWA

To get the archived version of a page closest to a particular date we can use the Memento API. The functions in this notebook smooth out these variations to provide a (mostly) consistent interface to the UK Web Archive, Australian Web Archive, New Zealand Web Archive, and the Internet Archive. They could be easily modified to work with other Memento-compliant repositories.