Removed misguided editing functionality from path_builder. If it's going to have container functionality it should be done properly (e.g. with iterators and by having path_builder meet the other requirements of a sequence container). Fixed up some minor issues with the io2d_error_category::message messages still having some TeX markup in them by accident. Changed to a noexcept macro check for easier maintenance of environment checks.
Changed path_builder::append_path name to path_builder::append. Added overload of path_builder::append that takes a const vector<path_data>& as a compromise for removing the editing functionality in the previous commit. Removed last direct uses of system_error ctor; everything now goes through the _Throw_if_failed_cairo_status_t helper function. Fixed _Throw_if_failed_cairo_status_t to properly construct an error_code to pass to the system_error ctor (it now uses io2d_category( )).