add hash params url= and iframe= to cog-basic example.

[bdon]

• enables loading arbitrary COGs and a cleaner UI for embedding in an iframe.

Could eventually be embedded in source.coop: see source-cooperative/source.coop#169

[kylebarron]

I agree there should be some generic viewer application, but I'm not sure I want this specific example to be that. In particular not sure I want this to be "depended on" by others; like I don't currently think of this example as a public API of the project

[bdon]

OK, makes sense - in that case I will work off cog-basic as an example in a different repository.

[kylebarron]

Awesome! In the future we can revisit this, but I want to focus on hardening the library first.

I took a pause here for a week to build async-geotiff, which has given me a much better low level understanding of various different profiles of GeoTIFFs. Now I think especially with #217 it'll help us make progress towards reliably rendering more types of COGs

[bdon]

I put a new generic viewer in a branch at https://github.com/cogeotiff/www.cogeo.org/tree/deckgl-cog-viewer