add ability to initialize with either a geotiff object or an arraybuffer directly alongwith URL

[Mihir Mone]

Atm the llibrary only allows passing in an url and options.

What do I do if I already have a parsed geotiff object or arraybuffer?

There seems to be a _parseTIFF function however, this can't be used since initialization fails if there is no URL.

Suggest making URL an optional parameter and then throwing the error in the draw phase if proper initialization was not done.