Fix recursion error on malformed use tags

[arthurdarcet]

<use> tags with an href attribute that isn't in the right namespace (xlink), trigger an infinite recursion error.

This PR introduce a ValueError for malfformed use tags, and lookup href attrs more leniently to support svg generated by some tools (chrome also support those mis-namespaced attributes, and the "lottie-web" framework generate svg files like this)

this fixes #187