-----------
Added format selection, use ``'PDF``' as default.
Added engines selection, use ``'dot'`` as default.
Added source encoding, use ``'UTF-8'`` as default.
Changed constructor arguments order, removed ``compile()`` and ``save()``-method,
reimplemented compilation in ``render()`` method, make interface more similar to
gv.3python (backwards incompatible change).
Double-quote-sign escaping, attribute list quoting.
``mkdirs()`` now correctly supports current directory filenames.