Docs
* Fixed broken links (to mdmetrics.com) in docs/* and README.rst
* Removed externally rendered formula (broken link) in BSPPthread.md
* Added explanation for tap module to README.rst
which also required a new image and a line in the docs/Makefile
CONTRIBUTING
* Added CONTRIBUTING (closes#3)
- explain structure of THREAD_TABLE.scad and relation to thread module
- explain threads and how to derive proper specs for inclusion in threadlib
- explain use of autogenerate.awk
- explain tests (i.e., test_table.awk)
closes#5