Add support for setting Ruby Net::HTTP read_timeout option separately

[springerigor]

Description

Right now timeout setting sets all the timeout values (read, open & write if available). To unify the API with Net::HTTP one (which has a dedicated method for read_timeout as well) I propose extending the RequestOptions by read_timeout.

[iMacTia]

Hi @springerigor, thanks for the addition.
I'm not sure why we were not supporting this yet, so thanks for adding it to the Net::HTTP adapter.
Do you think you might have some extra time to have a look at the other adapters and see if the new options can be easily supported there as well? This would help keeping them consistent as much as possible.

[technoweenie]

Hi @springerigor: You never replied, so I've continued work on it in #1022. Thanks for your help, I'll preserve your original commit :)

@iMacTia:

I'm not sure why we were not supporting this yet

I think you can track my understanding of HTTP timeouts through Faraday ;) Basically, :timeout was the original setting, while :write_timeout and :open_timeout came later as users had to set other timeout options. I don't think :read_timeout is required, but it's consistent with the other timeout settings. I suppose :timeout can stay as a default setting.