add m68k arch support

[knickish]

The M68k values were already included, this PR adds the enum Architecture entry for M68k and fills out the relevant match statements

[philipc]

Please also update

object/src/read/elf/relocation.rs

Line 244 in 61dc7b0

fn parse_relocation<Elf: FileHeader>(

and

object/tests/round_trip/mod.rs

Line 260 in 61dc7b0

fn elf_any() {

[knickish]

Thanks, had missed those functions. I believe I've gotten everything and matched the formatting.

[philipc]

Thanks!