Added association delete callbacks

You can now define a callbacks on a has_many or
has_and_belongs_to_many association that will be called
when an object is removed from the collection.
Merge pull request #103 from projecthydra/association_delete_callbacks

Added association delete callbacks
Add a test for association hooks on has_many relationships [log skip]
habtm#delete saves between the before and after hook.

When a has_and_belongs_to_many#delete method is called, the
relationships should be saved before the after_remove hook is called.
This enables the far side of the association to have the new
relationships in the after_remove hook.
Merge pull request #104 from projecthydra/save_between_hooks

habtm#delete saves between the before and after hook.
Backwards compatible change adding optional `args' param to ActiveFedora::SolrService.count,
enabling the method to pass args through to ActiveFedora::SolrService.query.
Merge pull request #105 from dchandekstark/solr-service-count-args

Add `args' param to ActiveFedora::SolrService.count
Test against rails 4.0.0.rc2
Adding CONTRIBUTORS and mailmap
Merge pull request #107 from projecthydra/adding-contributors-to-active-fedora

Adding CONTRIBUTORS and mailmap
Refactor test to use a model that makes sense conceptually [log skip]
Merge pull request #108 from projecthydra/refactor_test

Refactor test to use a model that makes sense conceptually [log skip]
Updated doc comment for .count to reflect change made in commit 1cd412a817f5d7b5c2f2cbc304b915b7423c499d.
Merge pull request #109 from dchandekstark/doc-fix

Updated doc comment for .count to reflect change made in commit 1cd412a8...
Removed redundant MacroReflection#klass method definition.
Removed some excessive whitespace.

Removed confusing examples using `composed_of'
Added method: ActiveFedora::Base#required?

Created ActiveFedora::Base#required? which, when given a field name,
tells you if the field is required or not.  It figures this out by
looking for a PresenceValidator (e.g. validates_presence_of) for the
field.

This is useful so that we can create dynamically generated forms and
determine whether any given field is required or not.
Merge pull request #110 from dchandekstark/macro-reflection-klass

Removed redundant MacroReflection#klass method definition.
Merge pull request #111 from projecthydra/required_test

Added method: ActiveFedora::Base#required?
Preparing for the 6.3.0 release
Added accepts_nested_attributes_for on RDFNodes