ADG canvas 0.8.0 released

ADG is a GObject-based library that provides a non-interactive cairo canvas specifically designed for generating technical drawings. More details can be found on its home page.

• The code shared by tests has been moved on an internal library (libadgtest) shared by both CPML and ADG.
• The test coverage is now checked by leveraging the Coveralls service provided by GitHub. The percentage has been raised from 53% to 94%.
• A fistful of bugs found while improving the test coverage has been corrected, most notably cpml_extents_is_inside(), cpml_segment_reverse() and some intersection algorithm.
• Children widgets now own weak references to parents, avoiding the circular dependency introduced by strong references.
• The overall sanity of the ADG library has been improved by adding additional checks where needed. The CPML library is not subject to those checks because by design it is not supposed to be sane.