Add "replPrompt" command to exercise checker

[benjaminselfridge]

There are lots of exercises/examples in Programming Cryptol like this one:

  Cryptol> take`{3} (12:[12])
  0
  Cryptol> drop`{3} (12:[12])
  12
  Cryptol> split`{3} (12:[12])
  [0, 0, 12]
  Cryptol> groupBy`{3} (12:[12])
  [0, 0, 1, 4]

Right now, the exercise checker can't handle this -- it only handles lines of input and expected output, but this mixes the two together. It would be pretty simple to handle this, by adding a new mode to the checker that looks for input and output at the same time, and distinguishes between the two by whether the line starts with Cryptol>.

[yav]

Good idea. Just a note that we may want to consider not just Cryptol> but also Float> and maybe other built-in modules to recognize Cryptol lines

[benjaminselfridge]

@yav Oh yeah, thanks.

[benjaminselfridge]

#1014