* Fix#1100
When the target Eigen3::Eigen is not present but could be found using
find_package() igl::core and igl::common link against the wrong TARGET
PkgConfig::Eigen3. Fixed this and also did some code cleanup.
* Drop support for PkgConfig
* Simplify configuration code
- Removed redundant call to find_package
- Removed LIBIGL_Eigen3_Target variable
- Echo status message
* Set libigl_common_FOUND if arget is OK
In libigl-config.cmake.in only libigl_core_FOUND was set, resulting in
an error if the user requested the igl::common feature, see #1077
* Replace target_link_libraries with set_target_properties
Otherwise cmake complains that the targets igl::core and igl::common are
not built by the current project.
* Also install .c files
Stefan Reinhold