Add initial ELF first load seg extension modifier

[rbs-jacob]

• [x] I have reviewed the OFRAK contributor guide and attest that this pull request is in accordance with it.

One sentence summary of this PR (This should go in the CHANGELOG!)

Add ELF modifier to reverse extend first load segment to the beginning of the ELF if it does not already.

[rbs-jacob]

To do:

• [ ] Test coverage
• [ ] Documentation