Turn on Rust lexing. Add a bigger sample

lib/linguist/languages.yml

@@ -1098,7 +1098,6 @@ Ruby:
 Rust:
   type: programming
   color: "#dea584"
-  lexer: Text only
   primary_extension: .rs
 
 SCSS:

samples/Rust/hello.rs

@@ -1,3 +0,0 @@
-fn main() { 
-    log "Hello, world!"; 
-}