Make raising signal exceptions a configurable option

Idea credit goes to @nevinera
Add ability to run all available jobs and exit
Use exit_on_complete instead of exit_on_empty_queue

This is just a little more descriptive of what actually happens under the hood.
Add new commands to the README
Move reporting and control code outside the loop callback block

This triggers a LocalJumpError in jruby
Test against Ruby 2.0.0
Convert text files to Markdown
Merge branch 'exit-when-done'

Conflicts:
	README.md
Merge branch 'signal-handling'
Prepare 3.0.5 release
Don't implicitly require simplecov
Update Code Climate badge [ci skip]
The source :rubygems is deprecated because HTTP requests are insecure.
Use AR's implementation of #encode_with which uses attributes instead of @attributes

As of Rails 3.2.12, they can return different things.
For example, if the `foorbars` table has an integer column called "size" with default 0 and not null:

f = Foobar.new
f.attributes["size"].class #=> Fixnum
f.instance_eval{@attributes}["size"].class #=> Arel::Nodes::SqlLiteral

This fixes an issue where:

Foobar.new.to_yaml

would raise an error:
ArgumentError: wrong number of arguments (2 for 1)
  from gems/arel-3.0.2/lib/arel/expressions.rb:3:in `count'
Merge pull request #479 from ngan/patch-1

Use AR#attributes instead of the instance variable
Fix attempt to update Psych encode_with
Added coveralls.io coverage badge
added coveralls gem, updated spec_helper
Merge pull request #485 from lemurheavy/master

Added code coverage badge.
updated coverage badge image / url

Uses https://coveralls.io/r/collectiveidea/delayed_job instead of the lemurheavy/delayed_job fork.