Cast integers with vim_eval
Cast integers with vim_eval

This makes it clearer/more strict altogether and is future-proof in the
sense that `vim.eval` might return integers for numbers in Vim after all.

See #553 for a very noisy discussion of what led to this.
Although it might be a regression in neovim-python after all it is good
to be on the safe side.

The bonus here is that we get "notified" in case of a option that is
expected to be an integer is a string instead.

Fixes https://github.com/davidhalter/jedi-vim/issues/553.

FBruynbroeck/jedi-vim,davidhalter/jedi-vim