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-0330.mediawiki

@@ -2,8 +2,8 @@
   BIP: 330
   Layer: Peer Services
   Title: Transaction announcements reconciliation
-  Author: Gleb Naumenko <naumenko.gs@gmail.com>
-          Pieter Wuille <pieter.wuille@gmail.com>
+  Authors: Gleb Naumenko <naumenko.gs@gmail.com>
+           Pieter Wuille <pieter.wuille@gmail.com>
   Status: Draft
   Type: Specification
   Created: 2019-09-25