Changes to keep inline with upstream Nengo.

 - `filter` => `synapse`
 - Deal with decoder solvers returning tuples

(cherry picked from commit b1796cb3d4562eb6eb6a422a2e0647489fdbef24)
Remove print statement from SDP Rx handler.
Pass the builder to node_builder `get_node_in_vertex` and `get_node_out_vertex`.
Factor `width` property out to provide `get_connection_width` in `edges.py`
Minor clean up, add `utils.py` for general utilities - consider moving/renaming at some later point.
Neaten `FilterVertex`, flake8.
flake8, neaten `NengoVertex`
Don't fail if  package not installed.
Builder calls `get_node_{in|out}_vertex` on the `node_builder` for the connection builder.
Change to assign Node transforms to `ReceiveVertex`s rather than Nodes themselves.
Correction to README.md for changes to SpiNNaker packaging.
[Bugfix] Input buffer accumulator assigns now use the mask correctly.

(cherry picked from commit 12f4e3257d07d03edf6bff6b1d2c5ab51bb309a9)
Changes to keep intrack with spin1_api changes (now version 1.3.0(-a?))
Merge branch 'master' into general-io

 - Changes to `README`
 - Inline with spin1_api changes

Conflicts:
	spinnaker_components/rx/dimension_source.c
	spinnaker_components/tx/tx-harness.c
Merge branch 'general-io' into general-io2
Correctly use defaultdict
[Bugfix] `stop` not `end` as attribute of Node Transform entry.
Remove unused `AssignedNodeBin` and supporting structures.