Port build-test
Port errors test
Remove unused function
Refactor timeslice to use a more sensible approach

It now represents a timeslice explicitly as start and end signal values.
Port build tests. Simplify and fix cycle()
Improve delay and timeslice dispose
Port filter and slice tests, fix takeWhile
Add timeslice tests
Export Stream type for back-compat
Port lift test, improve flatMapEnd dispose

Remove unused bits from stream-helper
Port MulticastSource tests

Scheduler.asap now returns a promise for the task result, which may be rejected due to task error.  Task errors propagate in "both" directions: to upstream via returned promise, to downstream via task.error
Port switch tests
Defer remaining tests, will update soon
Move remaining tests to appropriately named test files
Port periodic tests
Port delay-test, add timestamp

Add timestamp combinator which turns event values into { time, value } pairs.  Makes it easier to unit test time-related combinators and may be useful to users as well.

Expose timeslice() in public API
Port throttle tests
Add debounce tests
Add initial perf tests