Upgrade to nom 7 to get a clean rustsec audit

[jcfj]

Currently, using classfile-parser results in cargo audit complaining a little bit about a transitive dependency of the old nom.

Crate:     lexical-core
Version:   0.7.6
Warning:   unsound
Title:     Multiple soundness issues
Date:      2023-09-03
ID:        RUSTSEC-2023-0086
URL:       https://rustsec.org/advisories/RUSTSEC-2023-0086
Dependency tree:
lexical-core 0.7.6
└── nom 5.1.3
    └── classfile-parser 0.3.8

Sadly, the upgrade is far from small, since nom 7 removed macros.

[Palmr]

Sadly, the upgrade is far from small, since nom 7 removed macros.

Indeed, this is something I had a local branch for a long time ago but didn't finish.
So thanks for taking the time and effort 👍