Update elfio to the latest upstream version

[s3rvac]

We should consider updating elfio sources to the latest upstream version, which, at the time of writing, is 3.3.

[PeterMatula]

I was doing some diffs between our version and the latest ELFIO master. There are nontrivial changes in both. We cannot simply switch to upstream, because our changes often deal with nonstandard or damaged files.

It would be the best if we created a pull request with our changes on top of the latest ELFIO master. And then used the upstream if it gets merged.