I've also added some support for compiler errors in general, but these
will get expanded on later.
I've also quickly added a valgrind option to the tests and found a few
leaks. I'll deal with these later.
Summary of changes:
* Clarified the lifetime of the bytecode in memory
* Erroneous routines exit without compiling
* Empty VMs don't run
* Added a check for malformed assignments
* Renamed "routine" to "module" within the VM
* VM no longer tries to free the bytecode - must be done manually
* Started experimenting with valgrind, not yet ready
