This allows the LV2 source distribution to be used as an include path for
compilers and an LV2_PATH for applications, at the expense of self-contained
bundles.  That's a nice idea, but it made LV2 itself weird and annoying to
depend on.  This rearranges things so that directories in the source tree
correspond more closely to installation directories.

To make this possible, the "aux" directory in the documentation output has been
changed to "style", to avoid the reserved name "aux" on Windows.

These should have been added for the 1.18.4 release.  This seems a bit silly
for minor changes like this that span the entire project, but the documentation
tools currently require it.

Simplifying this would be nice, perhaps by using NEWS files as the canonical
source instead, which would be a nicer and more typical developer experience.

Since most applications pay to keep these ontologies in memory, it is best to
keep them small.  This replaces the "canonical" dcs ontology with a minimal and
restricted version specifically written for the subset of the vocabulary that
LV2 uses (like the xsd ontology).

Switches to safer and more modern idioms, and addresses many issues raised by
flake8 and pylint.