Fixes #1718

Initial commit. Still orienting on how to contribute.
It's building. Tests pass.

Before I continue, does the diff look sane?

I think I got the "public api" situated correctly.

The strangest thing I ran into was this error about default parameters. I'm not sure if this is pushing me towards adding a new method rather than an overload, e.g. StreamTrimWithMinId. I took out the default CommandFlags to build successfully.

error RS0026: Symbol 'StreamTrim' violates the backcompat requirement: 'Do not add multiple overloads with optional parameters'

I'm having trouble running the tests locally. I tried running the tests before making any changes and ~2/3 passed. It might be because I don't have all the versions of .net installed.