circumcentre() and det() methods added to class Triangle

Includes test for circumcentre()

Contributed by Vishal Tiwari

git-svn-id: http://svn.osgeo.org/geos/trunk@3912 5242fede-7e19-0410-aef8-94bd7d2200fb
Stub 3.5.0 section

git-svn-id: http://svn.osgeo.org/geos/trunk@3913 5242fede-7e19-0410-aef8-94bd7d2200fb
Configure Travis CI for GEOS (#657)

Configurations for GCC and clang with both Autotools and CMake.
Enable IRC notifications

Contributed by Mateusz Loskot <mateusz@loskot.net>

git-svn-id: http://svn.osgeo.org/geos/trunk@3914 5242fede-7e19-0410-aef8-94bd7d2200fb