Rename syntax definitions

Duplicate syntax definition names may cause problems.
Since nano comes with predefined all-lowercase syntax definitions,
we use uppercase letters everywhere to reduce the risk of future conflicts

rust.nanorc

@@ -2,7 +2,7 @@
 # Copyright 2015 The Rust Project Developers.
 #
 # NOTE: Rules are applied in order: later rules re-colorize matching text.
-syntax "rust" "\.rs"
+syntax "Rust" "\.rs"
 
 # function definition
 color magenta "fn [a-z0-9_]+"