Add .retriable feature to Http - Rebased

[tomprats]

Rebase of https://github.com/httprb/http/pull/598 with:

• hashrockets removed
• rubocop formatting updates
• creating a response with uri option

I don't understand the internals super well, but the changes I made off of the original were minor enough to not really change any actual functionality. Tests and cops all pass!

[tomprats]

I had some time, so I ended up rebasing and fixing the lint and test errors.

@ixti would you mind taking a look again?

[ixti]

That looks amazing! Thank you! Will take me some time reviewing though... :D

[tomprats]

@ixti Any luck?