Add a JS redirect preserving the fragment

[tbu-]

Also add a script that allows regenerating all of the documents.

[rust-highfive]

r? @alexcrichton

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[rust-highfive]

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[tbu-]

This should fix the issue mentioned in #5970 (comment).

[tbu-]

(I've tested locally, in Firefox, that the JS redirect takes precedence over the http-equiv redirect.)

[alexcrichton]

Thanks!