Now we don't have to manually remove this from the options hash since
the scope stores it outside of "options"

Remove the `options` reader from `Resource` because nobody needs to see
that hash.  Also remove mutations on the options hash in
`apply_common_behavior_for` because leaving the side effects in that
method makes it difficult to understand what is going on in the caller.

these two keys have a different merge strategy, and they also just get
removed from the options hash later in the code.  If we store them in a
separate place, then we don't need to remove them later

Eventually we don't want to expose the "options" hash from scope, only
read values from it.  Lets start by adding a reader method.

now we don't need to construct a Mapping object just to get an
ArgumentError if there is no `via` parameter provided.

We're going to try pulling this up further, and check `via` validity
sooner.  This way we don't have to do a bunch of processing on `options`
hashes only to find out that the route is incorrect

If we do the Regexp verification in a second method, then the
`split_constraints` method gets much easier.

I don't want `split_constraints` to mutate any instance variables.  That
way it's easier to move the method around and understand what it does
(it has no side effects)

I don't want to rely on mutating ivars.  This gives me more freedom when
refactoring

we don't need to do it so many times.

Now we only need to call `split_constraints` possibly twice!

apparently `format` can also come from the scope options, so we need to
extract it there too.

this way we don't have to insert / delete it from the options hash so
many times.

eventually we'll remove the need to access `scope` inside the Mapping
object.

`using_match_shorthand?` doesn't need to know that an options hash
exists.  Also use this opportunity to make the boolean logic a little
more sane

this simplifies the "downstream" logic since we know we'll only be
dealing with one particular type

I think we can find the original place where `action` is added to the
options hash now.

we want to try to pull this logic up to where the user actually passed
in "controller" so that it's close to the related call.  That way when
we're down the stack, we don't need to wonder "why are we doing this?"

There are some cases where :path is nil on option and we should respect
that.

We already know how to handle `path`, so lets just handle it on our own.

All callers of `action_path` interpolate the return value in to a
string, so there is no need for the method to to_s it.  to_sym on a
symbol will return the same symbol, though I think `action_path` may
always be called with a symbol so this might not be necessary.

we only need to check for `path` once.

Now we can see where `defaults` options originate

since `controller` and `controller_scope` were the same, just combine
them

This method isn't used internally, isn't tested, isn't documented.  We
should delete it.

add a predicate method so that we can avoid is_a? calls on the resource
object.

calling `scope` isn't cheap, so try to call cheaper methods that do the
same thing for those particular parameters (in this case `path_scope`)