rc modeline: Error out on unsupported formats

This commit makes `:modeline-parse` grab all lines that look like
modelines, and lets the parser deal with invalid formats.

This allows actually printing an error on unsupported modelines
formats, instead of ignoring them upfront.

rc/detection/modeline.kak

@@ -65,7 +65,7 @@ define-command -hidden modeline-parse-impl %{
         case "${kak_selection}" in
             *vi:*|*vim:*) type_selection="vim";;
             *kak:*|*kakoune:*) type_selection="kakoune";;
-            *) printf 'echo -debug Unsupported modeline format' \
+            *) printf 'echo -debug %s' "$(kakquote "Unsupported modeline format: ${kak_selection}")" \
                    | kak -p "${kak_session}"; exit 1 ;;
         esac
 
@@ -109,7 +109,7 @@ define-command -hidden modeline-parse-impl %{
 define-command modeline-parse -docstring "Read and interpret vi-format modelines at the beginning/end of the buffer" %{
     try %{ evaluate-commands -draft %{
         execute-keys <percent> "s(?S)\A(.+\n){,%opt{modelines}}|(.+\n){,%opt{modelines}}\z<ret>" \
-             s^\S*?\s+?(vim?|kak(oune)?):\s?[^\n]+<ret> <a-x>
+             s^\S*?\s+?\w+:\s?[^\n]+<ret> <a-x>
         evaluate-commands -draft -itersel modeline-parse-impl
     } }
 }