This tries to find the libbi executable; if this does not find libbi but it is installed, the location can be either passed to this function, or set globally via `options(path_to_libbi="/insert/full/path/here").
locate_libbi(path_to_libbi)
full path to the libbi executable as character string; if it is not found, an error is thrown
path to libbi, as either the path where the libbi executable resides, or the full path to the executable
Sebastian Funk