tests: Add more meaningful tests

[larsesser]

From the discussion of PR #19. It would be nice to have some minimal test cases exercising the interesting spots of the Schulze method.

An interesting test case that should be added is the following:

A>B>C
A>B>C
B>C>A
C>A>B

as it excercises the strongest path finding. 'A' and 'C' are indifferent to the voters, but the Schulze method returns 'A>B>C'.

PS: If we double these votes it's even more interesting as then 'C>A' pairwise, but the result is still 'A>B>C'.