Extend iteration methods to accept nodes
Implement function signature of `append`/`prepend`

...additionally, ensure that the methods do not throw errors when
invoked with `undefined`.
Implement function signature of `after`
Implement function signature of `before`
Implement function signature of `replaceWith`
Rename and simplify helper function

Because this helper does not create Cheerio objects, `makeCheerioArray`
is somewhat misleading. By instead declaring it as a recursive function,
it can operate on arrays and other objects, which obviates the need to
wrap arguments in array literals before invoking.
Merge pull request #290 from jugglinmike/manipulate-func-sig

Implement function signature for manipulation methods