109.55.00

- Fixed `Scheduler.is_running` to not initialize the scheduler.
- Added `Writer.make_write`, which is a general function for blitting
  directly to a writer's buffer.
- Added `Writer.transfer'`, which is like `Writer.transfer` but allows
  async actions in the callback.

  This was requested in pull request #1.
- Added `Writer.write_iobuf`, which blits the contents of an iobuf
  directly to a writer's buffer.