Initial work on new no-entity API

Not tested at all.
CanSet is wrong; no need to check for non empty tag
Begin goon testing app
Start some datastore tests
Don't memcache non existent entities on Get

At some point this should be added back (i.e., these entities get
memcached as not found somehow. Along with this, simplify greatly
transaction handling.
Fix wrong index check
Convert PutMulti to take interface{} instead of []interface{}
go fmt
Get and Put tests
Allow incomplete keys
Default Key() to no return nil on error
Just return whatever we get back
Update docs
Parent example
Specify that this is a goon error
Merge branch 'no-entity'

Conflicts:
	query.go