I've added the barest of search functionality.

The idea with Rustmax search is that is will be curated with topics related to Rustmax: crates, books and their chapters, standard library modules. Definitely not a full-text search like rustdoc; need to keep the index small.

Right now it only searches crates, books and standard library modules, by name or aliases.

I'll expand this basic search to be a bit more rich and robust with curated keywords etc; then augment it with things like function names, types, etc.