Don't use naiveSkipImpl.
Merge pull request #322 from PDAL/issues/317-naive-skip

Don't use naiveSkipImpl.
Add CONTRIBUTING.md

A CONTRIBUTING file can be useful for guiding new developers when they
are submitting changes, and Github supports
(https://github.com/blog/1184-contributing-guidelines) integration of
these CONTRIBUTING files into the pull request user interface.

This patch adds a basic CONTRIBUTING file.
Merge pull request #323 from gadomski/contributing

Add CONTRIBUTING.md
Merge remote-tracking branch 'upstream/master' into sbet-writer
Add some skeletons