Add information about Sidekiq to README

This adds a couple of lines to the README about Sidekiq, explaining that
it's possible to use `delayed_paperclip` with Sidekiq. It also explains
which queue Sidekiq has to listen to in order for the setup to work.
Merge pull request #50 from mrnugget/sidekiq_to_readme

Add information about Sidekiq to README
try to fix delayed_job version
Merge pull request #55 from maintux/master

fix for DelayedJob version
Fix process jobs for models with default_scope
Update specs to accept unscoped find chain
Merge pull request #58 from csaura/add-unscoped

Fix process jobs for models with default_scope
Added support for setting delayed_job queue
Fixed failing tests
Updated tests with new queue option
Merge pull request #59 from neilco/dj_queue_name

Added support for setting delayed_job queue
Update resque links in README.textile
Fix undefined method `[]' for nil:NilClass with Paperclip 3.5.2
Test to make sure tmp files are getting cleared
Merge pull request #68 from ScotterC/checking-tmp-files

Test to make sure tmp files are getting cleared
Merge pull request #67 from vdaubry/master

Fix undefined method `[]' for nil:NilClass with Paperclip 3.5.2
Merge pull request #65 from timbo/readme_update

Update resque links in README.textile
Allow processing some styles in foreground, some in background

Detect when only_process is set but different on has_attached_file and
process_in_background. In which case run foreground styles in normal hook,
and allow the backgrounded job to handle the styles on process_in_background
as normal.
Added test for split_processing option and explanation in README
Use ruby 2.0, p195.

Fixes many problems with rbenv users. rvm should be unchanged.