Nicknames do not allow for numeric characters

[miam-miam]

The following ballot fails to parse as one1 contains a 1

4 2
[nick one1 two three four]
[withdrawn two]
3 one1 three four 0
4 one1 three two 0
2 four one1=three 0
1 two 0
2 two=four=three one1 0
1 three four two 0
0
"Adam"
"Basil"
"Charlotte"
"Donald"
"Title"

With the following error:

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', /home/miam/.cargo/registry/src/index.crates.io-6f17d22bba15001f/stv-rs-0.2.0/src/parse.rs:87:44
stack backtrace:
   0: rust_begin_unwind
             at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/std/src/panicking.rs:593:5
   1: core::panicking::panic_fmt
             at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/panicking.rs:67:14
   2: core::panicking::panic
             at /rustc/d5c2e9c342b358556da91d61ed4133f6f50fc0c3/library/core/src/panicking.rs:117:5
   3: stv_rs::parse::parse_election
   4: stv_rs::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Nicknames should allow for numeric characters and should potentially even be optional.

[gendx]

This should be fixed in fb1f658 (included in the v0.3.0 release). Ultimately the parsing should be more robust than with regexes though.

Regarding making nicknames optional, the example in https://github.com/gendx/stv-rs/blob/main/examples/remove_nicknames.rs replaces them by integers, but indeed the parser doesn't allow such files yet.