Allow demongoization of strings to float

[ fix #3089 ]
Add range mongoization from hash

[ fix #3088 ]
Add support to exclude range

[ fix #3155 ]
ManyToMany handles primary_key option
Update changelog
make DocumentNotFound simpler to initialize

[fixes #3198]
Fix rake db:mongoid:drop_undefined_indexes

in fact, rename to remove_… for consistency, and deprecate the old name
remove drop_undefined_indexes deprecation
extracting persistence options
removing delegate from sessions
use class persistence_options when init document
adding proxy for better persistence_options on class level
small code cleanup
adding specs around sessions/options
small refactoring on sessions

collection should not have to deal with persistence options
Merge pull request #3038 from mongoid/session_options

Refectory on persistence options.
dont force I18n.locale to :en

[fixes #3169]
make threaded persistence_options private
make .ruby-vesion work on rvm and rbenv

ruby-*.*.* dont work on rbenv
2.0.0 dont work on rbenv

We need to define only the version and also the revision to make it work in rbenv
Update changelog