Remove leading `*' from defcustom doc-strings.

Remove leading `*' from defcustom doc-strings.
(esh-mode): Require it.
(esh-util): Use require rather than featurep and load.
(eshell): No need to test if eshell-mode is bound; remove obsolete
reference to eshell-auto.
(eshell-command, eshell-command-result): Don't require esh-mode
now that the file does.
(top-level): Move provide statement to the end of the
file.  Re-order and update commentary.