There is no need to allocate half a kilobyte of memory only check that a buffer
starts with a bunch of spaces and a `{`, 32b should be more than enough. Also,
no need to allocate it on the heap, having it on the stack works perfectly.
There is no need to detect the format and then the version when both can be
done at the same time.
Add a benchmark as well, on large and small atom and rss files.
