Raise clearer errors in case of failed requests

[Emerichenon]

[AnkurGel]

@Emerichenon Few tests break. Also, probably it's not a good idea to raise Uber::Error::BadRequest for every failure code. Making some changes :) // cc @sishen

[sishen]

@Emerichenon The error response will raise Farady::Error::ClientError. You can construct a friendly Uber::Error object in Client.rb#L138. Would you mind to update your PR there? Thank you.

[gabriel-dehan]

@AnkurGel Actual author here was working on a student's computer on a tight schedule while helping him with an uber relatied project. I'll make sure the tests passes or are you fixing it ?

@sishen Sure, we did not have much time so I didn't do the best fix in the world, I'll update it next week.

Cheers :)

[AnkurGel]

@sishen @gabriel-dehan Made some changes related to this here : https://github.com/sishen/uber-ruby/pull/21