Deterministic ordering in python < 3.6

[malramsay64]

Python 3.6 introduced a new dictionary implementation which retains order of insertion. This means
that the ordering of the dictionary and consequently the ordering of variable iteration is
deterministic.

In versions prior to this the ordering of variable iteration can vary between instances run.
This manifests itself as variation in ordering of commands, the difference between

echo 1 1
echo 1 2
echo 1 3
echo 2 1
echo 2 2
echo 2 3

and

echo 1 1
echo 2 1
echo 1 2
echo 2 2
echo 1 3
echo 2 3

This primarily poses an issue with testing, although it would be nice to remove random elements.

[malramsay64]

The appropriate data structure might be a named tuple since this also adds immutability which is currently assumed with the dict.