update to nom 4

[Geal]

Hello,

I'm currently testing the upgrade to nom 4 on various crates, to see if I forgot anything. Currently, I get these error after doing the following changes:

[Running 'cargo test']
    Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
     Running target/debug/deps/config-a0903495d12738cd

running 5 tests
test path::parser::test::test_subscript ... ok
test path::parser::test::test_subscript_neg ... ok
test path::parser::test::test_child ... FAILED
test path::parser::test::test_id_dash ... FAILED
test path::parser::test::test_id ... FAILED

failures:

---- path::parser::test::test_child stdout ----
        thread 'path::parser::test::test_child' panicked at 'called `Result::unwrap()` on an `Err` value: Complete', libcore/result.rs:945:5

---- path::parser::test::test_id_dash stdout ----
        thread 'path::parser::test::test_id_dash' panicked at 'called `Result::unwrap()` on an `Err` value: Complete', libcore/result.rs:945:5

---- path::parser::test::test_id stdout ----
        thread 'path::parser::test::test_id' panicked at 'called `Result::unwrap()` on an `Err` value: Complete', libcore/result.rs:945:5
note: Run with `RUST_BACKTRACE=1` for a backtrace.


failures:
    path::parser::test::test_child
    path::parser::test::test_id
    path::parser::test::test_id_dash

test result: FAILED. 2 passed; 3 failed; 0 ignored; 0 measured; 0 filtered out

error: test failed, to rerun pass '--lib'

They are probably linked to the new behaviour around partial data. It requires changing the input types, but makes all parsers easier to write.

[mehcode]

Thanks @Geal