Suggest `M-x enable-paredit-mode RET'.

The fragment above suggests autoloading `enable-paredit-mode', not
`paredit-mode', so `M-x paredit-mode RET' won't work too well...
Allow slurping while in a character.
If in a string, slurp into the enclosing list if necessary.
Add some slurp tests with characters and strings.
Make slurping and barfing support prefix arguments.

Positive numeric means slurp/barf that many forms.

Negative numeric slurp means barf -that many forms, and vice versa.

C-u means slurp/barf as many as possible before hitting end of list.

Tests are currently pretty limited.  Please help!
Tweak comment about barfage error.
Add news item about changes to HTML reference.
Note omission of `backward-down-list' in NEWS.
Note nicer slurpage into an empty list in NEWS.