Fix broken links in RFC 1884

These pages have gone 404, but seem worth preserving.
Linked to archive.org instead.

Author: intgr

text/1884-unstable-sort.md

@@ -67,7 +67,7 @@ A: Because it allocates additional memory.
 **Q: How much faster can unstable sort be?**<br>
 A: Sorting 10M 64-bit integers using [pdqsort][stjepang-pdqsort] (an
 unstable sort implementation) is **45% faster** than using `slice::sort`.
-Detailed benchmarks are [here](https://github.com/stjepang/pdqsort#extensive-benchmarks).
+Detailed benchmarks are [here](https://web.archive.org/web/20170316050341/https://github.com/stjepang/pdqsort#extensive-benchmarks).
 
 **Q: Can unstable sort benefit from allocation?**<br>
 A: Generally, no. There is no fundamental property in computer science saying so,
@@ -153,7 +153,7 @@ This algorithm still hasn't been built into in any programming language's
 standard library, but there are plans to include it into some C++ implementations.
 
 Among all these, pdqsort is the clear winner. Some benchmarks are available
-[here](https://github.com/stjepang/pdqsort#a-simple-benchmark).
+[here](https://web.archive.org/web/20170316050341/https://github.com/stjepang/pdqsort#a-simple-benchmark).
 
 **Q: Is `slice::sort` ever faster than pdqsort?**<br>
 A: Yes, there are a few cases where it is faster. For example, if the slice
@@ -217,5 +217,5 @@ has a fast unstable sort in standard library, so why shouldn't Rust, too?
 None.
 
 [orlp-pdqsort]: https://github.com/orlp/pdqsort
-[stjepang-pdqsort]: https://github.com/stjepang/pdqsort
-[blockquicksort]: http://drops.dagstuhl.de/opus/volltexte/2016/6389/pdf/LIPIcs-ESA-2016-38.pdf
+[stjepang-pdqsort]: https://web.archive.org/web/20170316050341/https://github.com/stjepang/pdqsort
+[blockquicksort]: https://drops.dagstuhl.de/opus/volltexte/2016/6389/pdf/LIPIcs-ESA-2016-38.pdf