Make `view-lossage' output of chars read from `read-char' more logical

Make `view-lossage' output of chars read from `read-char' more logical

* lisp/help.el (view-lossage): Use the new data format to output
data from `read-char' and the like in a more understandable
fashion (bug#21867).

* src/keyboard.c (command_loop_1): Record (in recent_keys) the end
of commands.
(Frecent_keys): Don't include `end-of-command' in non-command outputs.
(syms_of_keyboard): Define `end-of-command'.