Since I've had no luck finding a detailed Squirrel tutorial beyond embedding Squirrel and a few tidbits about the lexicon, I've taken it on myself to closely examine every aspect of the language through the limited (and admittedly weird) documentation and write an actual course with lessons, exercises, and projects to help people to familiarize themselves with the language. It's a work in progress right now, and later on, will also feature embedding and working with Squirrel from the C++ side. I'll later be adding an answer key as well for people to check their work with.
As of this post, I currently have three sections of the tutorial done, giving it a total of 15 lessons, and am currently working on the first project for it. I've also got some other free resources for use in games, including sprites, tilesets, sound effects, and a pixel font, all free to use. I'm also working on a game development kit aimed at hobbyists that will use Squirrel for scripting, so naturally, the lessons will come in handy with that.
For anyone interested in any of these things, head on over to http://kelvinshadewing.net and check it out!