Added automatic options result

Also checked that OPTIONS/HEAD method is actually allowed.

The user should have the option to disallow these (although we might want to make it that the user must specifically call disable_head/disable_options, so as to take more advantage of the default automatic response).

Having written the above, I note that the activity diagram that you included in documentation, shows 405 method not allowed response not being generated for GET or HEAD (and OPTIONS automatically gets a 200 OK response). So it would seem entirely reasonable that we DON'T allow the user to disable these responses (just as the code is doing now). However:

1) How do we enforce support for GET? (i.e. if there is a mapping for PUT, POST or DELETE, there is also one for GET?)
2) I can't find any support in the specification for this restriction on the 405 response.

So I'm inclined to think the logic is fine just as it is.