Add Adobe Font Metrics to recognised filetypes (#3731)

* Add Adobe Font Metrics to recognised filetypes

* Reduce filesizes of AFM samples

* Add a self-generated, unpruned AFM sample

lib/linguist/languages.yml

@@ -171,6 +171,18 @@ Ada:
   - ada2005
   ace_mode: ada
   language_id: 11
+Adobe Font Metrics:
+  type: data
+  tm_scope: source.afm
+  extensions:
+  - ".afm"
+  aliases:
+  - acfm
+  - adobe composite font metrics
+  - adobe multiple font metrics
+  - amfm
+  ace_mode: text
+  language_id: 147198098
 Agda:
   type: programming
   color: "#315665"