Fuzzy matching for Chicken AutoDoc and Completions

Because Chicken allows symbols to be imported with prefixes, and because 'apropos' does not provide any utility to match with the loaded prefixes, it is difficult to acquire information about prefixed symbols.

This solution hacks around the issue by providing naive fuzzy-matching. If no match for a symbol can be found then the first character is dropped and matching is attempted again; the process is repeated until matches are found or the entire symbol is consumed.

Also removes the (now redundant and slow) geiser-chicken-prefix-delimiters.