Manual/deterministic releasing of interface pointers

I wonder, is it possible to release a COM interface pointer manually by calling `Release()`, instead of waiting for its `__del__` to be called?

The problem of this method is that `Release()` is still called when `__del__` is called.

https://github.com/enthought/comtypes/blob/5c564eca9ec173fceafbdddd570fa5c7e1c6c564/comtypes/_post_coinit/unknwn.py#L272-L284

`__del__()` in Python cannot be used to achieve deterministic destruction, like destructors in C++ do. In the [docs](https://docs.python.org/3/reference/datamodel.html#object.__del__):

> __del__() can be invoked when arbitrary code is being executed, including from any arbitrary thread.

This would cause some problems if I want a certain COM object to be released at or before a certain time.

Although CPython uses reference counting, so *usually* the object will be released when the last reference is removed, it isn't necessarily the case in other Python implementations.

A common solution is to use the context manager. Implement `__enter__` and `__exit__`, so that it can be used in a `with` block, and be automatically released when leaving the `with` block. Many resource objects, such as files, already support the context manager protocol.