Host to Rx

From closed PR #5.
Changes are that:

1. Documentation has been added.
2. Routing key generation code added to the ReceiverVertex (SHA: a5eaba1c96eba2d0dc759e19ec91f742861e4b2d)
3. Finer grain control over which values are replaced (SHA: 8920b64c0675e1c6933de81f74b342eab56c3824)

I'll have a check on how to test this with SDP before we merge, but just to indicate the changes, here you go.