process: Author ↦ Authors

```
sed -z -i 's/Author: /Authors: /' bip-0*.md
sed -z -i 's/Author: /Authors: /' bip-0*.mediawiki
```

Also align correctly in case of multiple authors.

bip-0052.mediawiki

@@ -2,8 +2,8 @@
   BIP: 52
   Layer: Consensus (hard fork)
   Title: Durable, Low Energy Bitcoin PoW
-  Author: Michael Dubrovsky <mike+bip@powx.org>
-          Bogdan Penkovsky <bogdan+bip@powx.org>
+  Authors: Michael Dubrovsky <mike+bip@powx.org>
+           Bogdan Penkovsky <bogdan+bip@powx.org>
   Status: Draft
   Type: Specification
   Created: 2021-05-13