Remove unused 'Subtype' class.
Rip out old effect system.

It was a good experiment, but something better is planned.
WIP Implement SSA form and C backend
wip
wip
renaming or something
blah
wip
f move SSA types into its own module
FIX HTML THING
wip ssa
wip
things might work maybe
remove teh hack!
wip gadt on var/vartype
casting
more downcast
more prettyrr
move modules about
wip instantiate