Replaced data tables for binary functions with a custom matcher. Corrected one of P50 examples.

DataTables were causing test cases to prematurely signal success without
running all the examples. Couldn't find a way to test multiple data
tables in the same example group.
Added more examples and corrected method signatures of problems P55 to P63.
Corrected some tests. Changed order of examples to test base cases first.
Corrected P63 method signature.
Added more examples and corrected method signatures of problems P64 to P66.
Merge branch 'specs-only'