Add eshell-send-on-close-paren

Add eshell-send-on-close-paren

This defun attempts to emulate the genera repl, where a balanced closing paren
will execute the command.  Noticed some odd behavior with syntax-ppss giving
negative values for nesting occaionally.  May need to add in something with
syntax-ppss-flush-cache if the issue comes up again.  Otherwise looks to
function correctly.