Check overlapping quantization ranges before applying transfomation

[cirocosta]

Hey,

Although Quantize already includes tests for overlapping

asciinema-edit/editor/quantize_test.go

Lines 75 to 80 in c33b7f4

	It("overlaps if from in another range", func() {
	Expect(qRange.RangeOverlaps(editor.QuantizeRange{
	From: 1.5,
	To: 3,
	})).To(BeTrue())
	})

we don't make use of it after parsing the ranges.

We can make an O(n^2) checking over the ranges and that should be fine:

for i, _ := range ranges:
  for k, _ := range ranges:
    if i == k: continue
    if ranges[i].overlaps(ranges[k]):
       error

thx!

[cirocosta]

Similar to #11 , but instead, apply it only for the quantization transformation.