WIP: Filter readelf output

This MR serves as a use-case example, and should not be merged.

When comparing ELF files that have be recompiled in a non-reproducible way, there are many changes picked-up by diffoscope that may be irrelevant to analyzing the potential change in behavior of the program. The changes introduced in this MR try to mask some of those changes in the output of readelf. By combining theses changes with --exclude-command to ignore some sections (e.g. debug sections, comments, headers...), I sometimes divided the size of the output diff by a factor of 10.