And disable multi-patterns clauses. I was originally just controlling
whether we did disable that from the parser but then I figured we
could actually support multi-patterns clauses quite easily by simply
desugaring a multi-pattern into multiple clauses.
This is only a syntactic sugar, which means that the cost of writing
that on-chain is as expensive as writing the fully expanded form; yet
it seems like a useful shorthand; especially for short clause
expressions.
This commit however disables multi-pattern when clauses, which we do
not support in the code-generation. Instead, one pattern on tuples for
that.
KtorZ