vim syntax highlight for f2j

Highlight the f2j code in Vim editor.

Usage

Make sure Vim can idenfity the *.sf file type.

find $VIMRUNTIME/filetype.vim

add
```
" f2j

au BufNewFile,BufRead .*sf           setf f2j
```
For more details, type :help filetype in vim.
Put f2j.vim to $VIMRUNTIME/syntax/