Update resume table syntax

[dhil]

This patch changes the syntax of resume tables to match that of the reference interpreter, i.e.

resume $ct (tag $t $h)* => resume $ct (on $t $h)*
resume_throw $ct $e (tag $t $h)* => resume $ct $e (on $t $h)*

I have also updated the testsuite (by simply copying in the cont.wast from the reference interpreter). In doing so, I stumbled upon a bug in the wellformedness check for continuation types for which I have also included a fix.