natsort package misses some cases

[Ross Light]

Reporting on behalf of John Souvestre (thanks!), there are some test cases that the natsort package doesn't handle (listed are the expected outputs):

[]string{"a1", "a#1", "a_1", "aa"} ==> [a1 a#1 a_1 aa]
[]string{"1", "#1", "_1", "a"} ==> [1 #1 _1 a]
[]string{"1", "2", "01", "02", "3"} ==> [1 01 2 02 3]
[]string{"111111111111111111112", "111111111111111111113", "1111111111111111111120"} ==> [111111111111111111112 111111111111111111113 1111111111111111111120]

Marking as minor priority for now because these cases don't come up in cardcpx's use cases, but generally useful.