spatial_hub_connection_impl
===========================

Connection to a keyed\_representation target layer from a 
spatial\_representation
source layer. Sets the input of the target to the unnormalized (i.e., not divided by
length) spatial coding match of the source layer output to the ideal spatial
code given by converting the corresponding unit vector on the target layer to 
the spatial representation of the source.  Some relevant parameters are 
parameters of the spatial representation.

Parameters
----------

	parameter	default_value
	excitation	1
	inhibition	0

share_lookup
------------

	some_sphc share_lookup other_sphc

Attach `some_sphc` as another source of the target of another
spatial\_hub\_connection `other_sphc` and share cacheing data regarding the
ideal spatial code between the two.  The attachment will be to port 0.