Force permalinks to be lowercase and replace space and '_' with '-'

[choldgraf]

A common pattern in websites is to set all permalinks to be lowercase-with-hyphens. However since we're building permalinks from file paths, perhaps we don't want to force the files themselves to have this structure.

We could get around this by:

1. Automatically re-directing from the lowercase-permalink structure to whatever the file path capitalization etc
2. Automatically re-directing from whatever the file path capitalization is to lowercase-permalink (effectively forcing all pages to have a lowercase-permalink style URL.
3. Not addressing this at all

Anyone have thoughts on that? (cc @SamLau95...one of the main reasons for this is because the Data 8 textbook has mixed these two patterns over the years)

[choldgraf]

(my preference is probably for number 1)

[SamLau95]

I think 1) is good.

It might be confusing for authors to create a file HelloWorld.ipynb and have it automatically translated to hello-world. I think the actual filename should become the canonical URL (HelloWorld, even if it looks odd) and any redirects should go to the canonical URL (hello-world -> HelloWorld).

[choldgraf]

we're now automatically redirecting links to pages from the sanitized URL, so that these will always work