add: editorconfig (#1156)

Keep simple configuration synchronized between editors,
in order to hopefully keep diffs to more interesting changes.

.editorconfig

@@ -0,0 +1,31 @@
+# Consistent coding styles between different editors and IDEs
+# editorconfig.org
+
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = space
+indent_size = 4
+
+[*.md]
+# double whitespace at end of line
+# denotes a line break in Markdown
+trim_trailing_whitespace = false
+
+[*.yml]
+indent_size = 2
+
+# Ignore diffs/patches
+[*.{diff,patch}]
+end_of_line = unset
+insert_final_newline = unset
+trim_trailing_whitespace = unset
+
+
+# Ignore generated files
+[*.lock]
+indent_size = unset