Since this struct only contained function pointers, make all modules
export those functions directly.
The plugin manager now defines a module interface struct, and fills it
it by dlsym:ing the functions that used to be in module_info.
Since this struct only contained function pointers, make all particles
export those functions directly.
The plugin manager now defines a particle interface struct, and fills
it it by dlsym:ing the functions that used to be in particle_info.
Module plugins are (still) built in <build-dir>/modules.
When installing, f00bar binary is installed to <install-dir>/bin, and
the module plugins to <install-dir>/lib/f00bar.
For this to work, we now also set RPATH correctly. Since the installed
module plugins end up in a different location then when building,
different settings is required for BUILD_RPATH and INSTALL_RPATH.
