Natural sorting of indices in PrettyDiff output

[mewmew]

Hi @d4l3k,

First off. Thanks for sharing this library! It's exactly what I needed and really does the job well. I think it makes sense to fork a deep pretty-printed, and base the diff on that as you've done with go-spew.

After running messagediff.PrettyDiff on a few data sets, I noticed one aspect that could be improved with regards to the readability of the output. Currently array and slice indices are printed in lexicographic order, whereas natural sorting would make the output more intuitive.

For instance, the current output of messagediff.PrettyDiff is as follows:

modified: [0].Foo = 0x2
modified: [0].Bar = "asdf"
modified: [100].Foo = 0x2
modified: [100].Bar = "asdf"
modified: [101].Foo = 0x2
modified: [101].Bar = "asdf"
modified: [102].Foo = 0x2
modified: [102].Bar = "asdf"
modified: [103].Foo = 0x2
modified: [103].Bar = "asdf"
modified: [104].Foo = 0x2
modified: [104].Bar = "asdf"
modified: [105].Foo = 0x2
modified: [105].Bar = "asdf"
modified: [106].Foo = 0x2
modified: [106].Bar = "asdf"
modified: [107].Foo = 0x2
modified: [107].Bar = "asdf"
modified: [108].Foo = 0x2
modified: [108].Bar = "asdf"
modified: [109].Foo = 0x2
modified: [109].Bar = "asdf"
modified: [10].Foo = 0x2
modified: [10].Bar = "asdf"
modified: [110].Foo = 0x2
modified: [110].Bar = "asdf"

And with natural sorting applied, it would look as follows:

modified: [0].Bar = "asdf"
modified: [0].Foo = 0x2
modified: [10].Bar = "asdf"
modified: [10].Foo = 0x2
modified: [100].Bar = "asdf"
modified: [100].Foo = 0x2
modified: [101].Bar = "asdf"
modified: [101].Foo = 0x2
modified: [102].Bar = "asdf"
modified: [102].Foo = 0x2
modified: [103].Bar = "asdf"
modified: [103].Foo = 0x2
modified: [104].Bar = "asdf"
modified: [104].Foo = 0x2
modified: [105].Bar = "asdf"
modified: [105].Foo = 0x2
modified: [106].Bar = "asdf"
modified: [106].Foo = 0x2
modified: [107].Bar = "asdf"
modified: [107].Foo = 0x2
modified: [108].Bar = "asdf"
modified: [108].Foo = 0x2
modified: [109].Bar = "asdf"
modified: [109].Foo = 0x2
modified: [110].Bar = "asdf"
modified: [110].Foo = 0x2

For natural sorting, feel free to use any library you see fit, or for that matter copy over the implementation from https://github.com/llir/llvm/tree/master/internal/natsort which is based on @fvbommel's natural sorting package. The code is MIT licensed. (any code changes I did are released into the public domain).

Wish you all the best and happy times ahead!

Cheers,
Robin