feat: distinctUntilChanged operator

[tamazlykar]

Hi @raveclassic. Thanks for your lib.
I have a next example of usage of your library and wanna propose an operator for this.
const sortedElements = property.combine(data, elements, sortElements);
I have an array of some elements that should be sorted based on data. So when the data is updates i recalculate a new sortedElements, and it may have same order but different reference. So i need an ability to have a custom comparator function to omit some of the Property changes.

Looks like a distinctUntilChanged operator from rxjs can be a good fit for this, but with mandatory comparator, because frp-ts not emit when values has same reference.
I make an implementation of this function as proposal for example #58. So maybe it will be helpful for other devs too.
Can you take a look?

[raveclassic]

Let's continue the discussion here.
Ok so the use case is that you want to sort a list, but the Array.prototype.sort mutates the source array, right? It seems the correct way is to slice the source before sorting.