Deprecate then eliminate max/min

[icambron]

moment().min and moment().max were a good idea for helper functions, but combined with the mutability that most moment() methods have it turned out disasterously confusing.

So we're deprecating those two in favor of moment.min and moment.max, which are non-mutating and work on any number of objects:

// if a, b, c, d are moments ordered in time
moment.min(a, b);  // a
moment.min(a, b, c, d);  // a 
moment.min([a, b, c, d]);  // a
moment.max(a, b);  // b
moment.max(a, b, c, d);  // d
moment.max([a, b, c, d]);  // d

[ypresto]

moment().min(start).max(end) was useful for clamping.
Now it is moment.max(start, moment.min(end, moment()) and has less readability and long code.
How about adding moment().clamp(start, end)?

[icambron]

That seems easy enough to add from userspace. Untested, but:

moment.fn.clamp = function(start, end){
   return moment.max(start, moment.min(end, moment());
}

Since I suspect this is relatively rare use case and it's easy to do from userspace, I'd prefer to keep out of the lib in the name of limiting the surface area.