Add whereNotNull (#156)

This is useful during null safety migrations for the same reason as
`Iterable.whereNotNull` from `package:collection`.

update CI; prep for publishing (#155)

Prepare to publish (#126)

Prepare to publish (#104)

Prepare to publish (#94)

Drop non-extension methods (#88)

Prepare to publish as `1.0.0` with only the extension method
implementations. All deprecated methods are removed.

Temporarily drop build_runner. It was only for the example and
doesn't have a constraint allowing a breaking change in this
package.

Prepare to publish (#87)

Add asyncMapSample transform (#79)

Like `asyncMapBuffer` but drops instead of collecting previous events.

- Refactor `_Buffer` class into `Aggregate` which takes a function to
  aggregate values instead of only collecting them to a List. This will
  not be published.
- Add `asyncMapSample` which is effectively an identical implementation
  to `asyncMapBuffer` except it chooses a different aggregation
  function.

Enable and fix strict-raw-types checks (#78)

Most changes are in tests where we implicitly were using `<dynamic>` but
only ever passing a single type. Add specific types and clean up the few
cases where a different type from the norm was used. Extract utilities
for constructing both types of stream to do the tests in a loop, since
it's not using function literals anymore it can be a generic function.

In `lib/` add a few `<void>` type arguments for things like "trigger"
streams since we were never reading the value.