[pdal] Pipeline XML as primary channel?

[Pete Gadomski]

Mike,

> - Should we migrate XML format to use attributes?

I've been playing with pipeline xml for most of the day, and I'm a
huge fan. I'd vote for 'yes' for limited use of attributes, for a
couple of reasons:

* Readability suffers when everything is an element. The <Name> and
<Value> tags tend to blend together when I'm scanning a screen of
pipeline xml. I found that attributing the design added some useful
heterogeneity.
* Searching the tree is a little clumsy.
`//Filter[@type="filters.reprojection"]` seems cleaner than
`//Filter/Type[text()="filters.reprojection"/..`.
* <opinion>Attributes work well for atomic values e.g. driver types
and option names.</opinion>

As I was working with the XML today, I sketched up a couple of formats
to see what changes, if any, I would make. This design was my
favorite:

<WriterPipeline>
    <Writer type="drivers.oci.writer">
        <Option name="debug">true</Option>
        <Reader type="drivers.las.reader">
            <Option name="filename">in.las</Option>
        </Reader>
    </Writer>
</WriterPipeline>

Cheers,
Pete Gadomski