Faster public suffix domain parsing.

The scope of this library is limited to finding the tld+1 of a given domain from the public suffix list.

Approach:

• Load public suffix list entries into memory
• Match immutable, owned values of domains to be parsed
• Leverage a user-sized lru cache for entries

Goals:

• provide (mostly) compliant public suffix domain parsing.
• avoid allocations during domain parsing.
• offload as much work as possible to parsing stage.
• avoid depedencies that might themselves bring unwanted baggage
• inputs are not mutated, outputs are slices of inputs

Caveats:

• still rely on idna crate for punycode parsing
• we don't lower-case anything (for performance we ignore this)

Environment Variables

PUBLIC_SUFFIX_LIST_FILE=somefile - override which file will be loaded in place of public_suffix_list.dat

Example:

lazy_static! {
    static ref LIST: List = {
        let list = List::parse_source_file("public_suffix_list.dat", 10_000_000);
        list.expect("unable to parse PSL file")
    };
}

...

fn foo() {
    let domain = "abc.one.two.example.co.uk";
    let tldp1 = LIST.parse_domain(domain);
    
    assert_eq!(tldp1, Some("example.co.uk"));
}

TODO:

• benchmarks