Research more what options really are supported.
Accept --bnd-cbits and --bnd-inbits on command line.
Make one executable for nqueens which takes command line options.
Accept a limit of the number of boards to read on the command line.

This makes it easier to play with performance evaluation.
Added Bool representation for solving nqueens.

Also wrote an R script to make a graph of performance results for the
different representations using yices2.
Implemented text-based api z3 version of nqueens.
Wrote a script to automate yices2 graph generation.
Generated graphs for each kind of solver.
Increase bit size to 12 and fail if n is too large for Bit representation.
Minor cleanup of Sudoku.
Implemented normal Bit and Int cell representations.
Made a bargraph of sudoku performance.
Added profiling annotations to sketch evaluation.
Recognized a laziness problem in sketch implementation.

Made it explicit by introducing _|_, which causes many tests now to fail which
didn't before. Hopefully the fix will fix all the newly broken tests, and
others which were not working before.
Encapsulated evaluation monad.

In preparation for turning it into a proper error monad.
Reimplemented EvalMonad to be a proper error monad.
Updated test case status.
Minor cleanup.

Remove explicit error messages which should already have been caught by the
type checker.