Added a src/etc/vim/ftdetect directory and file.

Previously, in order to get vim's syntax highlighting,  you needed
to manually `:setf rust` on every file. Now vim will recognize *.rs
files as rust. This is a little nicer.

Author: tim

src/etc/vim/ftdetect/rust.vim

@@ -0,0 +1 @@
+au BufRead,BufNewFile *.rs    set filetype=rust