message: Add cfile::close()
diff: #ifndef VSNRAY_COMMON_CFILE_H
  #define VSNRAY_COMMON_CFILE_H 1
  +#include <cassert>
  #include <cstdio>
  #include <string>
  +#include <visionaray/detail/macros.h>
  +
  namespace visionaray
  {
  @@ -32,6 +35,16 @@ public:
  FILE* get() const { return file_; }
  bool good() const { return file_ != nullptr; }
  + void close()
  + {
  + assert(file_);
  +
  + int err = fclose(file_);
  +
  + assert(err == 0);
  +
  + VSNRAY_UNUSED(err);
  + }
  private:
  