Add option to show call signatures in command line

ftplugin/python/jedi.vim

@@ -25,7 +25,7 @@ if g:jedi#auto_initialization
         execute "nnoremap <silent> <buffer>".g:jedi#documentation_command." :call jedi#show_documentation()<CR>"
     endif
 
-    if g:jedi#show_call_signatures == 1 && has('conceal')
+    if g:jedi#show_call_signatures > 0 && has('conceal')
         call jedi#configure_call_signatures()
     endif