Fixed load_resource "find_by" in mongoid resources

Latest versions of Mongoid supports "find_by" query, but syntax
is slightly different than Active Record.
Refold generated Ability comments at 80 characters

A lot of people still fold their code at 80 characters, so it is
nice to have generated code consider this.
show build status fro master branch
add contributing guide

[ci skip]
Merge pull request #708 from calebthompson/patch-1

Refold generated Ability comments at 80 characters
Issue #687: cancan inserting "AND (NULL)" at the end of sql

Ensure that empty conditions does not trigger unmergeable conditions
Merge pull request #765 from jonsgreen/issue/cancan_inserting_and_null_687

Issue #687: cancan inserting "AND (NULL)" at the end of sql
add gem version badge (thanks Gemfury)
Working around CVE-2012-5664
Creating a Project here is unnecessary
added support for nested join conditions
releasing 1.6.9
Add docs for id_param option of load_resource

Added in https://github.com/ryanb/cancan/pull/425 but lacked documentation
Merge pull request #800 from wopata/master

Working around a SQL Injection Vulnerability in Ruby on Rails (CVE-2012-5664)
Merge pull request #806 from yuszuv/support_for_nested_joins

added support for nested join conditions
Merge pull request #705 from albertobajo/mongoid_find_by

Fixed load_resource "find_by" in mongoid resources
Merge pull request #728 from zephyr-dev/patch-1

Add docs for id_param option of load_resource