Warn when parsing XML on strings with unescaped XML entities

[ZevEisenberg]

If a string looks like <b>Gilbert</b> & <b>Sullivan</b>, the unescaped & will break XML parsing. The string must be escaped like this: <b>Gilbert</b> &amp; <b>Sullivan</b>. Other characters must be escaped too, as described here. Their solution:

extension String {
    var xmlEscaped: String {
        return replacingOccurrences(of: "&", with: "&")
            .replacingOccurrences(of: "\"", with: """)
            .replacingOccurrences(of: "'", with: "'")
            .replacingOccurrences(of: ">", with: ">")
            .replacingOccurrences(of: "<", with: "&lt;")
    }
}

This is fine, but also somewhat slow. It would be nice to:

1. Make something a little nicer/faster
2. See if we can detect unescaped entities and print some kind of warning.

[bonkowski]

The solution above will also escape the angle brackets.

[ZevEisenberg]

oof yes that is a glaring omission in my original post 😅

[bonkowski]

No worries, and thanks for the great library you have created 👍🏼