Allow custom Parsers to be defined for DataFrame.parser: GlobalParserOptions

[Jolanrensen]

Allowing users to set custom parsers would be very helpful. It could allow them things like:

class User(val name: String, val age: Int) {
    override fun toString() = "user-$name-$age"
}

DataFrame.parser.addCustomParser<User> {
    if (it.startsWith("user")) {
        val (_, name, age) = it.split("-")
        User(name, age)
    } else null
}

DataFrame.readCsv(myCustomUserData)

or we could even add an enum-specific variant. This can only be done with convert at the moment. It could allow immediate parsing of CSV -> enum for instance.

[Jolanrensen]

Additionally we should keep supporting the same arguments in ParserOptions to also allow the DF API to remain functional