add .editorconfig

EditorConfig is very well known config file for text editors/IDE's
with settings for project. This format supported by Vim, GNOME Builder,
Atom, Sublime and many others.

We will provide this configuration to be more friendly for newcomers.

Signed-off-by: Igor Gnatenko <i.gnatenko.brain@gmail.com>

.editorconfig

@@ -0,0 +1,14 @@
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+
+[*.[ch]]
+indent_style = tab
+indent_size = 8
+trim_trailing_whitespace = true
+
+[*.sym]
+indent_style = tab
+indent_size = 4
+trim_trailing_whitespace = true