Make all filetype names lowercase

This may be a breaking change if you are using a plugin that
checks the filetype. All the default plugins are now updated,
just make the filetype you were checking for previously all
lowercase.

runtime/syntax/tcl.micro

@@ -1,4 +1,4 @@
-syntax "TCL" "\.tcl$"
+syntax "tcl" "\.tcl$"
 header "^#!.*/(env +)?tclsh( |$)"
 
 ## Standard Tcl [info commands]