Leave the housekeeping to the NSHashTable itself, which should purge
null-references automatically (not necessarily right away)
Also update tests accordingly: Use `allObjects.count` instead of simply
`count` on the NSHashTable, since `allObjects.count` returns non-null
references.
This should fix#36
Fixes#30
Foreign attributes were handled incorrectly because attribute names
were implemented as pure strings without namespace prefix. This change
keeps the attributes as strings and eliminates any handling in regards
to namespaces.
Spec note about attributes:
"If designed today they would just have a name and value."
https://dom.spec.whatwg.org/#attr
For now these are ignored for faster testing/iterations.
The test fixture should also be replaced with several smaller
and more representative ones, since it is relatively big.
Building and testing the project via Xcode copies the resources into
the testing bundle, which is not the case for SwiftPM. Hence the helper
method, that tries loading the resource from the bundle first. If it is
nil then the resource is loaded from the test module path directly.