Fix rails_env option in schedules

As ENV['RAILS_ENV'] has been deprecated in Rails 3
and remove in Rails 3.1. I have left ENV['RAILS_ENV'] for backward
compatibility
first_in syntax added to the view
fixes
Fix can't convert Array into String exception when pass array args for rufus-scheduler every
provide correct yaml syntax for every and cron via Array in README
Add process tagging for scheduler process

On a server hosting multiple apps and multiple instances of
resque-scheduler, it can be difficult to tell which scheduler
goes with which app. This change adds an APP_NAME environment
variable that, if set, appends the app name to the procline.
Add 2 methods:
* Resque.delayed? MyJob => Boolean
* Resque.next_delayed_schedule MyJob => timestamp
Use resque redis namespace
added description in README doc for rake task to load with environment

Added description in README doc for rake task to load with environment

Well Personally I have do this because my `Resque` was using a different connection other then the default `redis://127.0.0.1:6379` so I set my Redis connection to Resque in initializer like this 

`Resque.redis = Redis.new( )` 

Now this work well with resque and redis connection is picked up correctly but when resque_scheduler without environment it does not take the redis connection into consideration and dies of "Connection Timeout" because `resque_scheduler` rake task does not load the environment so in use case like this it is important to load the rake task along with environment something like this 

`rake environment resque_scheduler`
resque-scheduler.gemspec: updated redis version specifier
Merge branch 'master' into delayed

Conflicts:
	lib/resque_scheduler.rb
Merge pull request #231 from nkondratyev/patch-1

Updated redis version specifier
Locking rufus-scheduler dependency to ~> 2.0

as referenced in #264, which I'm planning to leave open until this
dependency can be bumped to `~> 3.0`.
Merge pull request #265 from meatballhat/rufus-scheduler-lockdown

Locking rufus-scheduler dependency to ~> 2.0
Bumping a proper amount.  Should have looked at the danged diff :scream_cat:
Updating HISTORY with notes for v2.2.0
Bumping version by a patch level
Updating per version requirement changes

[ci skip]
Specify MIT license in gemspec

Closes #266

Thanks, @bf4!
Use Resque.validate instead of custom .validate_job!

Job class validation is now a part of resque API.
No need for custom method anymore

Adapted from #181 submitted by @bogdan