Respect RFC-7234 Caching Headers

[Koshroy]

Having the document loader fetch documents to resolve IRIs constantly can get pretty expensive from a network bandwidth perspective. If there's interest, I can make a PR to add RFC-7234 support for caching.

[kazarena]

Hi @Koshroy, yes please make a PR. That would be great!

[kazarena]

This feature has been implemented by @Koshroy.