This implements a basic version of the algorithm from: Luc Maranget,
[Compiling pattern matching to good decision
trees](http://moscova.inria.fr/~maranget/papers/ml05e-maranget.pdf). No
heuristics are used - the first column is always chosen.
* Closes#1798
* Closes#1225
* Closes#1926
* Adds a global `--no-coverage` option which turns off coverage checking
in favour of generating runtime failures
* Changes the representation of Match patterns in JuvixCore to achieve a
more streamlined implementation
* Adds options to the Core pipeline