Add .editorconfig to tell editors/IDEs basic whitespace rules.

https://editorconfig.org/ is a common file that is understood
by virtually all editors and IDES that deal with code. With this
file, contributors to the code-base already have a good head-start
complying with the expected formatting rules.

Note, this also includes a trim_trailing_whitespace setting, that
will remove random whitespace at end of lines, which will reduce
merge conflicts on such lines. Some existing files have spurious
whitespace at the end of lines, so whenever they are edited first
under .editorconfig configuration they will be cleaned up.

Signed-off-by: Henner Zeller <[email protected]>

Author: hzeller

.editorconfig

@@ -0,0 +1,13 @@
+# Editor config file, see http://editorconfig.org/
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{h,c,cpp}]
+indent_style = space
+indent_size = 4
+