Added support for hidden Input fields and views: WP_Hidden_Field and WP_Hidden_Field_View.
Autoload classes
Merge pull request #20 from jesinwp/autoload-classes

Autoload classes
Add storage factory and registry.
Added STORAGE_TYPE constant.
Updated WP_Html_Element->get_attributes_html() to output value when value is an attribute.
Renamed Registry items to entries.
Merge remote-tracking branch 'origin/master'
Refactored and reformatted autoloader.
Call for contributors and additional info
Link contributing section
Removed strtolower() in autoloader and used proper class names instead.
Merge remote-tracking branch 'origin/master'
Add base styles.
Merge pull request #26 from devinsays/css-styles

Add base styles.
Added saving post metadata.
Merge remote-tracking branch 'origin/master'
Removed hardcoded plugin directory in the wp_enqueue_style() call.
Changed $object_type->object_type to $object_type->class for clarity.
Worked on Object Type while documenting it on the wiki.
- Renamed $object_type->object_type property to $class.
- Removed has_subtype element from  array of WP_Object_Type::$_core_object_types.
- Renamed WP_Object_Type::$_core_object_types to $_object_type_classes
- Renamed $object_type->register_object_type() to register_class()
- Added register_object_type_class() function.
- Renamed $object_type->assign_type() to assign()
- Removed option to pass a non-qualified object type class to $object->assign_type() to avoid edge case ambiguity since custom classes can be registered.
- Changed all references of 'all' subtype to be 'any' and initialized empty subtypes to have a value of `any'.
- Fixed code for $object_type->is_equivalent()
Added WP_Field_Base->input_feature()
Renamed WP_Field_Feature_Base->html_element to be just element
Added get_input_html() and input_feature() to WP_Field_View_Base plus
Changed WP_Field_View_Base->get_features_html() to call  $this->get_input_html() instead of  $feature->get_feature_html() for input feature.
Added register_field_type() and register_autoload_class()
Added WP_Metadata::register_autoload_class() and modified to just class static vs. local static, and prefixed with underscore to imply hidden.
Added static modified to _enqueue_admin_styles().
Added leading underscore to autoloader method name.