* Iterates two slices and diffs them.
* Params:
* a = a forward sliceable range
* b = a forward sliceable range
* equalSpan = an EqualSpan
* Elements from a and b must be comparable for equality.
* If equalSpan is Drop (the default), then only Diff structs with Insert,
* Delete, or Replace tags will be returned; otherwise Diff structs
* covering all the input will be returned, so will additionally include
* Diff structs with Equal tags.
* Returns: A slice of Diff structs.
* Iterates two slices and diffs them. * Params: * a = a forward sliceable range * b = a forward sliceable range * equalSpan = an EqualSpan * Elements from a and b must be comparable for equality. * If equalSpan is Drop (the default), then only Diff structs with Insert, * Delete, or Replace tags will be returned; otherwise Diff structs * covering all the input will be returned, so will additionally include * Diff structs with Equal tags. * Returns: A slice of Diff structs.