Add a Python version of make_bootable
Created originally on Bitbucket by flameeyes (Diego Elio Pettenò)
Was already merged in Bitbucket before import, marked as merged by the import user
My version of make_bootable works for all filesystems without needing dd, and without needing an external checksummer.
While it depends on numpy it could be possible to improve it to not require it. And then it would work on Linux, OSX and Windows with a single, non-compiled binary.