Add serde feature

[abhillman]

Adds serde derivations when that feature is enabled for Record and its recursive children types. Example:

use std::fs::File;
use serde_json;
use zoneparser::ZoneParser;

fn main() {
    let file = File::open("my-zone.no").unwrap();
    let parser = ZoneParser::new(&file, "my-zone.no");
    
    // Collect all records
    let records: Vec<_> = parser.collect::<Result<Vec<_>, _>>().unwrap();
    
    // Serialize to JSON
    let json = serde_json::to_string_pretty(&records).unwrap();
    println!("{}", json);
}

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Run the additional test via cargo test --features serde serde. Use the additional feature in Cargo.toml via:

cargo add zoneparser --features serde

or

zoneparser = { version = "0.1.6", features = ["serde"] }

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In addition, this PR has respective commits that:

• commit the result of cargo fmt
• updates the bstr dep to its latest version in Cargo.toml
• adds Cargo.lock (standard practice)
• updates to README.md

For reviewing ease, optionally review one commit at a time.

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Thanks for the nice code and for publishing it. I had written a parser earlier this year in Rust as well and like what you have done here.

[erikoest]

Thanks for your contribution. I'll consider adding it in. But could you please remove the 'cargo fmt' changes from your feature branch? It would make it easier to see what are the real changes that you introduce. I can rather add formatting/prettyprinting in a separate commit later.