Potrace 1.16 released

September 17, 2019: Release 1.16

This release consists of bugfixes and minor portability improvements.
A potential arithmetic overflow was fixed. Rotation angles are now
normalized to between -180 and 180. We now use binary file I/O on the
OS/2 platform. The test suite tolerances were adjusted. The
configuration option --enable-local-getopt was renamed as
--with-included-getopt. Some build system improvements. Thanks to
Henri Salo and Dave Yeo for reporting bugs and suggesting
improvements.