Small fixes

Fixes:

* Off by two error when encoding is utf8
* Makes call to `Godef(...)` silent when called from under cursor (saves having to hit enter to acknowledge)
* Always use a `tempname()` file (this is relatively [standard practice](https://github.com/majutsushi/tagbar/blob/master/autoload/tagbar.vim#L2000-L2003))
* Delete the `tempfile` once created
* Use `writefile` to avoid triggering any events (e.g. [`vim-gocode`](https://github.com/Blackrush/vim-gocode) reformats on a `:w`

Thanks