Normalize line endings to LF; add .gitattributes and .editorconfig

.editorconfig

@@ -0,0 +1,20 @@
+# Editor defaults for ITFlow - see CONTRIBUTING.md ("Style")
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
+
+[*.md]
+trim_trailing_whitespace = false
+
+# Vendored - do not reformat
+[libs/**]
+indent_style = unset
+indent_size = unset
+trim_trailing_whitespace = false
+insert_final_newline = false