Add option to limit number of points written in Translate, using
Decimation filter modification. Remove count from all other kernels
(except Random, where it us used in the FauxReader).
change m_limit to point_count_t and remove template types, which are inferred
Merge pull request #536 from PDAL/issues/535-write-fixed-point-count

Add option to limit number of points written in Translate