entity: better doc for TO_ARRAY constants [closes #46]
repository: fixed identity map saving

I don't understand how can I missed that. Sorry.
relationships: fixed removing entity with compulsory foreign key
exceptions: added NullValueException
propertyContainer: fixed handling NULL value from storage
relationships: renamed variable
relationships: rewrite to use NullValueException
entity: implemented hasValue for IPropertyContainer (API BC break!)
relationships: hasMany: fixed saving collection retrieved from cache
relationships: fixed persisting cached relationships
mapper: removed leading dot

Nette database does not strip this dot.
This triggered error in postgre, mysql was ok with that.
doc: the first try to start somehow
entity: added isAttached() method [closes #52] (interface BC break!)
entity: removed getForeignKey (replaced by getRawValue())
entity: introduced IPropertyHasRawValue [refs #53]
entity: DateTimePropertyContainer implements IPropertyHasRawValue [refs #53]

BC break - now returns unix timestamp or null.
entity: getRawValue() removed from IProperty[Container|Injection] [refs #53]
relationships: removed getPrimaryValue method() (BC break!)
repository: call onBeforePersist before geting loaded relationships [closes #48]

change: before events are called always, others only if entity was changed
entity: added enum constant existence validation checking [closes #47]