correctness tests

[sebfisch]

Create a binary that parses and executes AT&T's regression tests.

[sebfisch]

initial implementation: cd3148c2037869de5fe4c80ab070dfed61f935e3.

AT&T tests would still be worthwile.

[sebfisch]

We could use QuickCheck or SmallCheck to test properties like the following:

• epsilon R == R
• R epsilon == R
• (RS)T == R(ST)
• (R | S) | T == R | (S | T)
• R | S == S | R
• (R | S)T == RT | ST
• R(S | T) == RS | RT
• R* == epsilon | RR*
• R* == epsilon | R*R
• R* == R* R*

[sebfisch]

QuickCheck tests for equivalence of algorithm with specification are in src/quickcheck.lhs