Generate test.browser.js even if tests fail.
Simplify Context#delegateYield by expanding scope of ContinueSentinel.

Returning the ContinueSentinel object used to have the same effect as
continuing the while loop inside the inner function (or, equivalently,
breaking out of the switch statement), but it turns out to be more
convenient if we jump back out to the level of the .next or .throw method
and do everything except calling assertCanInvoke() again.
Mostly unify .next and .throw into a single helper method.
Inline handleDelegate into the .next/.throw helper function.
Inline invoke into helper function and rename helper to invoke.
Use invoke.bind to create generator.next and .throw methods.
Set state to GenStateSuspendedYield after first delegate iteration.

The idea here is that the parent generator is now effectively suspended at
a yield point within the delegate generator.
Inline assertCanInvoke into invoke.
When a newborn generator is sent a value, throw a TypeError.

Closes #76.