[pdal] Some user requests

[Michael P. Gerlek]

I had a talk with a potential/future PDAL user last night. We do much of what he needs already, but three lacking areas we identified are:

* We need an ascii/xyz reader. (We already have a writer.)

* We need a "geotiff reader" -- more generally, we need a way to take 2D X,Y gridded data as input (where the value at each cell is, say, Z) and treat that as arbitrary point data. This would be done via GDAL, so any rastery format would work. (and I suppose we ought to take in OGR points too...)

* We need a Python wrapper around PDAL, so people can use PDAL to read data in from wherever but then process the points themselves using custom code, most likely in numpy. [Howard discussed this exact issue last week as well.]

-mpg