Add support for other URL shortener services

[rahulkp220]

I was thinking of extending this package to offer many other services as well as using bit.ly for instance.In that case,

• We may rename the package to suit the needs, something like URLShortener.jl
• Use multiple dispatch to expose a single function that takes in a long URL and a name of a shortening service, although some services require auth tokens. Can be an issue of discussion.