Task: J2N.Character.CodePointAt(char[], int, int): Convert limit parameter to length (a .NET convention)

[NightOwl888]

This is a breaking API change that will require a major version bump.

Current API:

namespace J2N
{
    public static class Character
    {
        public static int CodePointAt(this char[] seq, int index, int limit)
    }
}

Desired API:

namespace J2N
{
    public static class Character
    {
        public static int CodePointAt(this char[] seq, int index, int length)
    }
}

Of course, the business logic needs to change to accommodate this fix.