tree: add vimrc and editorconfig

Imported from ostree.

Closes: #1029
Approved by: cgwalters

.editorconfig

@@ -0,0 +1,5 @@
+[*.[ch]]
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true
+indent_brace_style = gnu

.vimrc

@@ -0,0 +1,12 @@
+set expandtab
+set tabstop=8
+set softtabstop=2
+set shiftwidth=2
+
+" Let's try to not go longer than 92
+set textwidth=92
+autocmd BufNewFile,BufRead *.c,*.h set textwidth=92
+
+" This is the same as the default minus 0{, which is really annoying otherwise
+" with our coding style.
+set cinkeys=0},0),:,0#,!^F,o,O,e