Fixes indentation in tree macro's case statement
Removes `attr_accessible` macro as mass assignment is no longer handled in mongoid 4.0
Changes `inc` to mongoids new syntax
Changes runtime dependency to support mongoid 4.0
Replaces `Node.index_options` with the new `Node.index_specification` method
Updates statement about the mongoid version in README.md
Merge branch 'master' into mongoid-4.0
Merge branch 'master' into mongoid-4.0
Change the scope to be a proc wrapped critera.

Scopes in Mongoid 4 must be procs that wrap criteria objects.
Merge pull request #50 from madwire/mongoid-4.0

Change the scope to be a proc wrapped critera.
Updates .travis.yml to match the one of mongoid
Adds depth field to fix the ordering issues with ancestors. Closes #52.
Requires Ruby standard library when running the specs on Rubinius
Only use rubysl-rake as a dependency instead of the whole rubysl
Merge branch 'mongoid-4.0'
Updates readme to reflect compatibility with mongoid 3.x
Adds note about upgrading to mongoid-tree 2.0
Merge branch 'master' of github.com:benedikt/mongoid-tree
Prepares mongoid-tree 2.0.0 release
Upgrades to RSpec 3