Added method to delete specific table entry rather than table.delete()

[b-becker-k]

Changes the behaviour of the delete method when called from a specific table entry.
Currently running

p = mro.table.select_one("name='TestName'")
p.delete()

is equivalent to

p.table.delete()

This adds a delete method to database entry custom classes in the same way the update or create was done, which generates a clause based on the entry's primary keys to only delete this specific entry.
eg, if the table has primary keys id and name;

p = mro.table.select_one("name='TestName'")
p.delete()

is now equivalent to;

p = mro.table.select_one("name='TestName'")
mro.table.delete('id=%s and name=%s', 12, 'TestName')