Hello,

When migrating from my old eshell configuration into using `setopt', I
noticed a discrepency in the docstring of
`eshell-scroll-to-bottom-on-input' and its customization type (the
docstring says t and 'all should be equivalent, whereas the type does
not allow t at all), hence I started looking into fixing issues around
the `defcustom' calls in eshell.

Here attached is a draft patch to update eshell defcustoms.  The commit
message contains a long [TODO] section outlining all my ideas on how to
change a given portion, but these ideas probably need more input.

Patch based on 34ac7d90876, 4-5 days old master.