Migrate internal usage off deprecated interfaces

This introduces the following changes:

* `.portstr` -> `.name`
* `.setRTS()` -> `.rts`
* `.getSettingsDict()` -> `.get_settings()`
* `.applySettingsDict()` -> `.apply_settings()`
* `.inWaiting()` -> `.in_waiting`
* `.isOpen()` -> `.is_open`

In addition, the test suite's `DummySerial` class is updated,
and commented-out code is updated.