Minor doc change: Rails usage

I figure I'd change the setup file to a more idiomatic Rails usage: an initializer.
Delete hash.rb

This is on account of two things:

1) a bug I saw when the app gets preloaded and I try to request anything with an integer that uses `#to_query`.

For example, `url_for(test: 1)` will throw an exception "undefined method `gsub' for 1:Fixnum"

2) As we know, monkey-patches are bad practice. If we really want to use an alternate `#to_query`  method, we should really use a utility class instead. But since Rails 3 implements `#to_query` already, we should remove this file altogether.
remove /rgigya/hash.rb include
Also, get tests back up by including activesupport's to_query method.
Update gemspec to handle removal of hash.rb
Add a few more error codes to raise custom exceptions when changing a user's password.
Add error code exception names.
Add credits to method.
Add tests for new exceptions.
Merge pull request #2 from sfsekaran/patch-1

Minor doc change: Rails usage
Merge pull request #3 from sfsekaran/patch-2

Delete hash.rb
Merge pull request #5 from markrickert/more-exceptions

Adds more exceptions