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-0132.mediawiki

@@ -1,7 +1,7 @@
 <pre>
   BIP: 132
   Title: Committee-based BIP Acceptance Process
-  Author: Andy Chase <theandychase@gmail.com>
+  Authors: Andy Chase <theandychase@gmail.com>
   Status: Closed
   Type: Process
   Created: 2015-08-31