Fix update and update_all examples to property set fields.
extending documentation about relation callbacks

adding an example and other useful information
Fix spelling: geospacial => geospatial
Merge pull request #231 from herimedia/niels-spellingfixes

Fix spelling: geospacial => geospatial
Small change on ruby version doc on mongoid/index
Make 3.1.0 the version on install page
Merge pull request #230 from danielpietzsch/relationCallbacksExtension

Extending documentation about relation callbacks
Merge pull request #229 from jpmckinney/patch-1

Fix update and update_all examples to property set fields.
Update install docs for Rails 4

A few references didn't exactly match what is expected in
a Rails 4 app. I've kept the 3.2 references and added 4.0
Fix awkward sentence structure in safe mode description.
Merge pull request #235 from Billiam/fixes/safe-mode

Fix awkward sentence structure in safe mode description.
Rails 4 has dropped ActiveResource.

Amend mongoid/installation to mention about this.

[Closes #219]
Fixed a link to the "One Spec to Rule them All"

In https://github.com/mongoid/mongoid/commit/01ed3f6ec6e39cd938c5b66be29a19875a679620#diff-bb1b905fa1adea594d0d1aacadce9582,

This file:
https://github.com/mongoid/mongoid/blob/master/spec/mongoid/nested_attributes_spec.rb

Was moved to:
https://github.com/mongoid/mongoid/blob/master/spec/mongoid/attributes/nested_spec.rb
Merge pull request #237 from adammeghji/patch-1

Fixed a link to the "One Spec to Rule them All"
Updating docs that use hash arguments instead of multiple params
Use ruby 2.1.0
Better Rakefile
Show latest version on installation
Remove redirect rules

we dont need them anymore.
see mongoid/mongoid.github.com#5
update tips page. fix grammar mistake