Previously, the state was updated before writing the output (up to the current
time), so output "in the past" would be incorrectly written based on the
current state.  This fixes that by switching things around, so the output is
first written up to the current time, then the state is updated (and the loop
continues).

This takes advantage of the fact that write_output() effectively does nothing
with a zero length.

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.

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