Update outdated deps

[CosmicHorrorDev]

This pull request updates error-chain, hex, and reqwest to their most recently release version while dropping serde_derive and url_serde by using features to expose the same functionality on the base crates instead.

This was all of the low hanging fruit where the only complicated update was with reqwest (done in a separate commit) which involved some basic changes around Urls and switching to the blocking::Client to still mimic the old behavior since the async client is now the default. The plan is to eventually expose both sync and async functions in the future.

Not included in this PR is switching away from error-chain (preferably to thiserror). error-chain is no longer maintained (the github repo now lives under rust-lang-deprecated as an archived repo). I haven't switched away quite yet because it will be a pretty blatant breaking change with error-chain exposing an error type that includes an ErrorKind which is pretty unique compared to the standard way of exposing errors now, so it's possible that we want to do a release before switching away from error-chain

[CosmicHorrorDev]

Sorry I don't mean to be a bother. Just trying to make sure that This PR and #34 didn't slip through the cracks. Both of them are pretty small changes that shouldn't take much time to review

[samiraguiar]

Please @compressed, take a few minutes to review this and the other PR. I was happy to see new commits when I checked this repo, but got turned off again to see PRs pending for months now.