chore: add .editorconfig and .gitattributes

Every tracked text file is already LF; this keeps it that way on Windows.

Author: Seungpyo1007

.editorconfig

@@ -0,0 +1,15 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
+
+[*.{yml,yaml,json,toml,html}]
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false

.gitattributes

@@ -0,0 +1 @@
+* text=auto eol=lf