Add union example to specifc examples

So that we have something to test with.
Improve node usage in refTypeSubRenderer

We match the approach in the index.py CompoundTypeSubRenderer as
improved by danielmatz.

In fact we really should refactor so that the same code is used in both
locations if at all possible. Else they'll fall out of sync.

We also change from using the self.data_object.kind to using
file_data.compounddef.kind for the identifying string (class, union,
etc.) This means that instead of looking at the stirng on the reference,
we wait to parse the data that is being referenced and dig down a level
to the compounddef and look at the kind on that.
Refactor compound rendering code into shared function

Used for both top level CompoundTypeSubRenderer and RefTypeSubRenderer
which both reference data in a separate file and read the file and
formation the content. Forcing both to use one function helps them not
to drift out of sync.
Update README

It had fallen out of the sync in a number of ways. We also stop
pretending that we have a testsuite.
Merge branch 'compound'