Handle sections by category, not by name

[PaoloS02]

As suggested in issue #117 in order to avoid ambiguity when selecting the sections for the size benchmark, we should select them by category rather then by name.
Categories selected through options --text, --data, --rodata and --bss should be grouped by looking at the attributes of the sections, like for elf the flags: SHF_WRITE, SHF_ALLOC, SHF_EXECINSTR.
The same should apply to the macho format, with its own flags (advice on this is welcome).

[Roger-Shepherd]

This requires input from someone with either macho expertise or some time. I've found it difficult to locate up-to-date macho documentation. Even the lief sources don't appear to be completely up-to-date.....

This proposal also raises the issue of whether to/how to maintain backward compatibility. This was a consideration for the way in which macho handling has been added.