comparables have `isGreaterThan`/`isGreaterThanOrE...

# strikt

[Eric]

comparables have `isGreaterThan`/`isGreaterThanOrEqualTo`/etc assertions but no check if equal using compareTo which is useful for things like BigDecimal
maybe add this?

fun <T : Comparable<T>> Assertion.Builder<T>.compareToEqual(expected: T) =
    assert("is equal using compareTo to %s", expected) {
        if (it.compareTo(expected) == 0) pass() else fail()
    }