let inlining in goal printing

[samcowger]

This implements a new primitive, print_goal_inline :: [Int] -> ProofScript (). print_goal_inline, provided a list of numbers, prints the current goal while inlining the memoization variables that would otherwise be assigned a number in the provided list.

[eddywestbrook]

Please add a haddock for print_goal_inline. You can just copy the doc string for it in the interpreter. Also, it would be good to think about how to test this functionality, though testing printing is always a bear. Otherwise, these changes look good to me!