Support field type object non absolute hrefs

@fosrias @miwest929 @sheavalentine-mdsol Please review and merge.

Some issues reported by @ejennings-mdsol 

In short: 
1) Two api docs in api_descriptors directory:
```yaml
id: DRDs1
semantics:
  name:
    doc:...

id: DRDs2
safe:
  search:
     parameters:
       - href: DRDs1#name
```
When running `rdlint --all` - lint will complain that `DRDs1#name` is not found in registry. Because lint was processing documents one by one without loading both at the same time.

2) Field_type object is now supported.

@sheavalentine-mdsol this will indicate to load all documents in directory into the registry.
Dereferencer will be able to find them.