Squashed commit of the following:

commit 810935058699f01b08cbbf64f3cb59679932e158
Author: Pete Gadomski <pete.gadomski@gmail.com>
Date:   Thu Aug 14 19:19:31 2014 +0000

    Add the rxp reader

    RXP is the streaming file format used by RIEGL Laser Measurement Systems
    (http://www.riegl.com). Support for reading rxp
    files is provided by RiVLib, RIEGL's own library which they release for
    use by their customers.

    RiVLib only supports reading rxp files, not writing them.