database slot indexes

[evri...@core.gen.tr]

Hi

Today I've fixed database slot indexes and find-object-with-slot method.
Now it returns the first match, also i've added find-objects-with-slot with
returns all objects matching a certain slot-value.

This naturally leaded me to fix defcrud macro. Ive added class.query
method to defcrud which returns an intersection set. class.find returns
again the first match. Aycan encouraged me to implement a better function
query like (database.query *db* goal-p bfs-dfs)

I hope i'll find time to implement such.

Updated the documentation to reflect crud change:
http://labs.core.gen.tr/#databaseprogramming

evrim.