add .editorconfig

.editorconfig

+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+
+[meson.build]
+indent_size = 2
+tab_size = 2
+indent_style = space
+
+[*.{c,h}]
+indent_size = 4
+tab_size = 4
+indent_style = space
+max_line_length = 80
+
+[*.xml]
+indent_size = 2
+tab_size = 2
+indent_style = space