This helper tool uses BBEdit's Preview Windows to preview Markdown syntax in your rustdocs. It has the following components:
- A binary Preview Filter
- The source for the filter, written in Rust, as a binary in the toolbox
- The Preview CSS that uses the classes outputted by the filter
This will start transitioning the impl generator to be a more generic helper tool, with the impl generator as one of its component.
Also, drop the "-bin" from the name, because what else is it going to be?
This makes it possible for users to upgrade with a simple `git pull`,
rather than having to re-download the latest release from GitHub each
time - after checking that there is one, first!
It also converts it from just a `.bblm` file to an entire `.bbprojectd`
file, allowing me to add things like Clippings and Text Filters in the
future. (Planned!)
