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-0093.mediawiki

@@ -2,8 +2,8 @@
   BIP: 93
   Layer: Applications
   Title: codex32: Checksummed SSSS-aware BIP32 seeds
-  Author: Leon Olsson Curr and Pearlwort Sneed <pearlwort@wpsoftware.net>
-          Andrew Poelstra <andrew.poelstra@gmail.com>
+  Authors: Leon Olsson Curr and Pearlwort Sneed <pearlwort@wpsoftware.net>
+           Andrew Poelstra <andrew.poelstra@gmail.com>
   Status: Draft
   Type: Informational
   Created: 2023-02-13