make stripe-listify-buffer and stripe-org-table-enable interactive
mention stripes-org-table-enable in README

Instead of the old name `org-table-stripes-enable'.
add turn-on-stripe-buffer-mode

This allows turning on `stripe-buffer-mode' without turning on
`hl-line-mode' at the same time.

Update documentation accordingly (also removing obsolete information
about hl-line+).