Update sorted function to natural sort based on child.text value

[rrajpuro]

Fixes issue #153

Adding a lambda function key to return child.text so we can sort strings naturally.

Reasons for choosing natural sort over lexicographical sort:

• ACL sequence numbers
• Interface numbers (Ex: Sort interface Vlan2 before interface Vlan100)

[jtdub]

natsort is an external dependency that would need to be installed to use use this fix. I'm not certain that we want to add the external required dependencies.

[aedwardstx]

@rrajpuro thank you for your interest and suggestion.

Children can be weighted via OrderRules such that they float to the top or sink to the bottom relative to other children in the same level of the hierarchy. Otherwise, children retain their original order. As much as practical, we want to retain the order of config lines from the original config text. When different sorting logic is required, I’d recommend creating a post_load_callback, or similar approach, to handle these special cases.

Also, we want to keep external dependencies to a minimum.

[rrajpuro]

Hello!
I agree with the point about keeping external dependencies to a minimum.
But then, what is the point of the sort method?
sorted(self.children) does not sort these Hconfig objects

should we implement the __ne__, __lt__, __gt__, __le__, __ge__ methods?

Also, I was working on fixing a unified_diff behaviour. The all_children_sorted method does not work as expected there. Hence, unified_diff needs this or a similar fix.

[rrajpuro]

        for child in sorted(self.children):

I have two alternatives for removing natsort dependency and fixing this

1. Use the usual string compare:

        for child in sorted(self.children, key=lambda child: child.text):

2. Use the simplest form of natural sort:

convert = lambda text: int(text) if text.isdigit() else text
alphanum_key = lambda key: [convert(c) for c in re.split('([0-9]+)', key.text)]
...
...
        for child in sorted(self.children, key=alphanum_key):

Let me know if any of these is preferrable.