New command, no byte compilation errors, autoload comments

These commits add:

- no byte compilation errors, caused mainly by assignments to free variables,
- autoload comments for some interactive functions to use howdoi without `(require 'howdoi)` form,
- a new command which insert a code snippet in the current buffer for given query.

Note: I didn't add any keybinding for the new command.

I hope I didn't break anything.