* make is usable as a CMake sub-project
  * put options in a separate namespace
  * but use parent project values when specified
* always specify COMPONENT when INSTALLing
* don't use PROJECT_SOURCE_DIR/PROJECT_BINARY_DIR

Also

* fix out-of-source builds (don't generate files
  in the CMAKE_SOURCE_DIR, always do it in CMAKE_BINARY_DIR)
* make subsequence cmake runs less verbose, use MESSAGE1
  to avoid repeating messages that didn't change