Add Standard ML to languages

lib/linguist/languages.yml

@@ -637,6 +637,14 @@ Smarty:
   extensions:
   - .tpl
 
+Standard ML:
+  lexer: OCaml
+  aliases:
+  - sml
+  extensions:
+  - .sig
+  - .sml
+
 SuperCollider:
   lexer: Text only
   extensions:

lib/linguist/mimes.yml

@@ -50,3 +50,4 @@ image/x-icns @icns
 text/cache-manifest @manifest
 text/plain @cu,cxx
 text/x-nimrod @nim
+text/x-ocaml @ml,mli,mll,mly,sig,sml