Set .editorconfig for .xs files and add modeline to APItest.xs

Author: leonerd

.editorconfig

@@ -8,3 +8,12 @@ tab_width = 8
 end_of_line = lf
 trim_trailing_whitespace = true
 insert_final_newline = true
+
+[**/*.xs]
+charset = utf-8
+indent_style = space
+indent_size = 4
+tab_width = 8
+end_of_line = lf
+trim_trailing_whitespace = true
+insert_final_newline = true

ext/XS-APItest/APItest.xs

@@ -1,3 +1,7 @@
+/*
+ * ex: set ts=8 sts=4 sw=4 et:
+ */
+
 #define PERL_IN_XS_APITEST
 
 /* We want to be able to test things that aren't API yet. */