Add maker for 'go build' and golint.

I'm not really sure how to handle the `/dev/null` stuff though. Syntastic has a utility function that returns `NUL` or `/dev/null` depending on OS:

```vim
function! syntastic#util#isRunningWindows()
    return has('win16') || has('win32') || has('win64')
endfunction

function! syntastic#util#DevNull()
    if syntastic#util#isRunningWindows()
        return 'NUL'
    endif
    return '/dev/null'
endfunction
```

https://github.com/scrooloose/syntastic/blob/master/autoload/syntastic/util.vim#L20