sorry, my mistake
Revert "use CMAKE_INSTALL_PREFIX instead of CMAKE_BINARY_DIR ..."

This reverts commit d5b9335a5ae588ad3655c82bef98efb2cc1bb078.
Fixed mistake in libstp install location (not sure how it worked before)
and added comment that
CMAKE_ARCHIVE_OUTPUT_DIRECTORY and CMAKE_LIBRARY_OUTPUT_DIRECTORY
are build locations **not** install locations.