[pdal] PdalXML style

[Michael P. Gerlek]

Which of these is best for representing the options block of a pipeline
description:

(A) Options block is a tree of elements

<Writer type="drivers.las.writer">
        <Options>
                <filename>out.laz</filename>
                <compression>true</compression>
        </Options>
        <Reader type="drivers.las.reader">
                <Options>
                        <filename>in.las</filename>
                </Options>
        </Reader>
</Writer>


(B) Options block is an element with attributes

<Writer type="drivers.las.writer">
        <Options filename="out.laz" compression="true"/>
        <Reader type="drivers.las.reader">
                <Options filename="in.las"/>
                </Options>
        </Reader>
</Writer>


(C) Options block is just attributes on the stage

<Writer type="drivers.las.writer" filename="out.laz" compression="true">
        <Reader type="drivers.las.reader" filename="in.las>
        </Reader>
</Writer>


-mpg