keep only one Faraday::Connection regardless of endpoint

Special endpoints (such as search, upload) are handled per-request.
Merge pull request #266 from mislav/endpoint

keep only one Faraday::Connection regardless of endpoint
Make aliases more consistent between classes
Rename lazy_attr_reader to attr_reader since it's not actually lazy
Allow multiple arguments (and return an array) for the following methods

* Twitter::Client#accept
* Twitter::Client#block
* Twitter::Client#deny
* Twitter::Client#direct_message
* Twitter::Client#direct_message_destroy
* Twitter::Client#disable_notifications
* Twitter::Client#enable_notifications
* Twitter::Client#favorite
* Twitter::Client#follow
* Twitter::Client#oembed
* Twitter::Client#report_spam
* Twitter::Client#retweet
* Twitter::Client#saved_search
* Twitter::Client#saved_search_destroy
* Twitter::Client#status
* Twitter::Client#status_activity
* Twitter::Client#status_destroy
* Twitter::Client#status_with_activity
* Twitter::Client#unblock
* Twitter::Client#unfavorite
* Twitter::Client#unfollow
Sort into columns
Format in three columns
Add note about threading
Clean up README
Update rate limit example [ci skip]
Splat

Closes #267.
Change default adapter to net-http-persistent
Rename TwitterOAuth middleware to OAuth middleware
Remove untested gateway middleware

TODO: Allow modifications to middleware stack for people who want to
continue using the library to talk to gateways.
Fix bug in specs

I have no idea how this bug ever would have been caught without using
code coverage tools.
Coverage of gif uploads
Add specs for error class
Remove Twitter::Error::EnhanceYourCalm

The new Twitter Search API endpoint (api.twitter.com) never returns HTTP
status 420. Instead, it returns HTTP 400 (which throws a
Twitter::Error::BadRequest).
Add note about removing gateway support
Add note about removing Twitter::Error::EnhanceYourCalm [ci skip]