Merge branch 'master' into f-of-t-nodes
Simulator queries IO to determine whether Node output needs to be transmitted.
Added ability to precompute output for Nodes which are a function of time.

- New APLX nengo_value_source to inject precomputed values into simulation
- New Vertex ValueSourceVertex to precompute Node values
- Config options `f_of_t` and `f_period` for periodic and aperiodic functions of time
# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
# On branch f-of-t-nodes
# Changes to be committed:
#	new file:   ../examples/fn_t_node.py
#	modified:   ../nengo_spinnaker/builder.py
#	modified:   ../nengo_spinnaker/config.py
#	new file:   ../nengo_spinnaker/nodes/value_source_vertex.py
#	modified:   ../nengo_spinnaker/simulator.py
#	modified:   Makefile
#	new file:   value_source/Makefile
#	new file:   value_source/slots.h
#	new file:   value_source/value_source.c
#	new file:   value_source/value_source.h
#
Merge branch 'master' into f-of-t-nodes

Conflicts:
	nengo_spinnaker/builder.py
	nengo_spinnaker/simulator.py
Fix recursive bug in totuple.  Not sure how it got there.
[Bugfix] SDPReceiveVertex reserved too little space for output keys.
Fixes to transmitted multidimensional values from ethernet.
Initial stab at decoded value recording.
Merge branch 'master' into decoded-rec
Merge branch 'master' into f-of-t-nodes
Example transmits sin rather than constant value.
Add decoded value example.
Default synapse value if not specified on probe.
Correct interleaving of probed decoded value data.
Remove debug io_printfs, "neaten" pointer arithmetic(?)
Corrections to SDP Receive Vertex, try to transmit output every timestep.
Neaten decoded value probe example.
ValueSourceVertex correctly calculates number of dimensions and hence block size.
Merge branch 'master' into decoded-rec
bitarray is an optional extra.

Without bitarray, utils.probes.SpikeProbe is None, this is caught by the
builder and an error is raised if the user tries to make use of this
functionality.