dillon1000/react

Inline reactive scope dep checks; no more change vars

Reactive scopes are currently preceded by individual variable declarations, one 
for each of the scope's dependencies. Only after checking independently if each 
of these dependencies has changed do we then do an "or" to check if we should 
actually recompute the body of the scope. 

But that's wasteful: it's more efficient to rely on `||` short-circuiting, and 
recompute as soon as any input changes. 

The main reason I can see not to do this is debugging. Having the change 
variables makes it easy to see what changed. But at this point I think it makes 
sense to optimize for code size and performance; we can always add back a 
dev-only mode that uses change variables if that turns out to help debugging.