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

sed.nanorc

@@ -1,4 +1,4 @@
-syntax "sed" "\.sed$"
+syntax "SED" "\.sed$"
 header "^#!.*bin/(env +)?sed( |$)"
 
 color red "[|^$.*+]"