Adds start of runnables.
Internalises exception init/exit and cleans up test.c.
Renames test to testMain.
Adds new test, ifdef guards on runnable.h's optional features.
Adds runnable test.
Stuff. Gonna rewrite imminently.
Most of the rewrite, plus a lua test. Still needs actual implementation, though.
Implementation + tests done for runnables.