Ignore vendor specific tags under paths

Vendor specific tags are now ignored at the path level. Vendor specific tags are any tag of the form "x-something": <some object>

The intention here is to allow the vendor specific tag to apply to all paths.

E.g.

...
paths:
  x-product: "Favorites"
  /posts/{id}:
    get:
      ...
    put:
      ...
...