Implement `$.prototype.addBack`
Return a fully-qualified Function from `$.load`

The function generated by `$.load` should inherit from the `Function`
prototype so that methods like `call`, `apply`, and `bind` are available
to users.
Merge pull request #552 from jugglinmike/load-function

Return a fully-qualified Function from `$.load`
Correct error in documentation

The current documentation of the `map` method demonstrates an incorrect
usage. Because the function creates a Cheerio object containing the
values returned by the iterator function, the current example
demonstrates creating a Cheerio object whose members are themselves
Cheerio objects. The behavior of the `html` method invoked on such an
object is not defined.

Update the example to demonstrate a simpler, more tradition use of the
`map` method.
Merge pull request #556 from jugglinmike/fix-map-docs

Correct error in documentation
Expose DOM level 1 API for Node-like objects

Now that htmlparser2's default DomHandler supports the `withDomLvl1`
option, enable it by default for all parsed content.

Update the project documentation and tests to use this standard API to
exemplify usage.
Add explicit tests for DOM level 1 API

Instead of implicitly relying on other unit tests to exhaustively assert
the "shape" of the Node-like object's API, define a single test to
ensure that the documented properties are available and functioning as
expected.
Merge pull request #561 from jugglinmike/dom-lvl-1-2

Expose DOM level 1 API for Node-like objects
Merge pull request #527 from jugglinmike/add-back

Implement `$.prototype.addBack`
fix lint error