* fixes go-openapi#94

* now expanded $ref are always contained in the resulting document.
  All circular $ref that used to resolve to a remote $ref now resolve
  as a json pointer inside the expanded document.
* schema IDs are removed from the expanded spec: schemas expanded from some schema ID reference
  now refer to the new expanded root document.
* fixed circular ID resolution

Signed-off-by: Frederic BIDON <[email protected]>

* fixes go-openapi#94

* now expanded $ref's are always contained in the resulting document.
  All circular $ref that used to resolve to a remote $ref now resolve
  as a json pointer inside the expanded document. Pointer resolution
  prefers pointers to definitions.

* added additional test case for remote cyclical $ref, from azure API

* schema IDs are removed from the expanded spec: schemas expanded from some schema ID reference
  now refer to the new expanded root document.

* circular IDs are resolved against the corresponding root document.

> NOTE(1): uncovered pre-existing issue with nested schema ID involving cyclical references.
> This case remains unsupported and is illustrated by test case: circular_test.go#L198 ("withID")

> NOTE(2): pre-existing issue with non-deterministic expansion remains unsolved,
> although the election of the replacing pointer inside the root document
> somewhat reduces the scope of this problem.
>
> This case remains illustrated by a minimal test case: circular_test.go#L46 ("minimal"),
> which expands correctly, but with changing results.

> NOTE(3): notice that expansion is still not an idempotent transform, in the presence
> of cyclical $ref's: another run on an expanded spec with remaining cyclical $ref
> will expand further down and detect again the cycle.
>
> The result remains functionally correct, as illustrated by test case: circular_test.go#L168 ("CircularID").
> Notice that this test case reproduces a validation fixture from jsonschema test (passed by go-openapi/validate).

Signed-off-by: Frederic BIDON <[email protected]>