Send more keys with VimuxSendKeys

[slowkow]

This patch addresses issue #44, where @gberenfield says:

I can't seem to paste in around 30-40 lines of code into my vimux repl.
Anything less works fine.

I write the selected text to a temporary file, read the file with tmux,
and paste the contents into the appropriate window.

Caveats:

• When sending the text, vim prompts you with a more screen in which you
  must press Enter repeatedly to scroll to the end. The text is actually sent
  after you're done mashing the Enter button. I haven't found a way around
  this -- I'm new to Vimscript.

[slowkow]

After applying c1c4e3a, I use this function to send code chunks over to my ipython session in an adjacent tmux pane:

" Send selected text to an adjacent tmux pane.
function! VimuxSlime()
  " Automatically register a tmux pane.
  if !exists("g:VimuxRunnerIndex")
    call VimuxOpenRunner()
  endif
  " Suppress the `more` screen with "Press Enter".
  silent call VimuxSendText("%cpaste\n".@v."\n--\n")
endfunction
" Yank the selection into the v register and call the function.
vmap <Leader>g "vy :call VimuxSlime() <CR>

[alerque]

Thanks for taking the time to contribute. I hope others find this useful, but it's going to need a bit of tweaking before merging for everyone.

1. We need some way around the "mashing enter" caveat. I don't know off hand what that can be, but maybe other contributors know?

2. The hard coded temp file path needs to detect relevant default system temp file paths and test that it's writable before going down that road. Many systems are not going to be able to blindly write to the root tmp directory, and we don't want to stop working places we currently function.

[alerque]

See #115 for what looks like a much more elegant fix to the same problem. I'm not sure why it got closed, possible because the author was frustrated with the inactivity, but I think it needs to be reviewed again in light of the issue and compared to this solution.