This change adds support for function calls. We do not yet wire it
into the various function call expressions, however, that should be
relatively trivial after this change. (It is dependent on figuring
out the runtime representation of load location objects and subsequent
uses of them). This change also updates the scoping logic to respect
"activation frame" style of lexical scoping, where an inner function
as a result of a call should not have access to the callee context.
This change also includes logic to detect unhandled exceptions and to
print an error as a result. Eventually, we will want stack traces here.
cff883211b