put DESDATA_LENGTH and DESDATA_OFFSET in metadata #568
Add PDAL_ADD_TEST cmake macro

This macro can be used to add test executables to the project.
Especially useful for plugins.
Update PDAL_ADD_PLUGIN target_link_libraries

Remove PCL_LIBRARIES and add PDAL_LINKAGE.
fix copy/paste bug in drivers.las.writer for CreationDOY/CreationYear
Merge pull request #568 from PDAL/issues/568-desdata-offset-length

PDAL pipeline serialializtion does not contain DESDATA_OFFSET or DESDATA_LENGTH since Nitro
Merge pull request #573 from gadomski/plugin-marco-changes

Plugin marco changes
link PCL_LIBRARIES for PCL plugins after tweak in #573