renamed Halibut::HAL to Halibut::Core
I forgot to commit again, didn't I? tests are green.

So, I've been reading POODR, right?
I've been progressing _really_ slowly, so despite not even having
finished Ch03 I've decided to try my hand at this sort of "dependency
inversion"
renaming load/dump to parse/render
set_property is private for later deprecation (possibly). see Resource#[]=