append new elements for each element in selection

fixes #438
fixed context of `this` in .html
add `muted` attr to booleanAttributes
sorted
Fixed a bug in removing type="hidden" attr

If you try to remove the type attribute from inputs when it's set to `hidden` Cheerio incorrectly assumes that it's boolean.

If I understand what `rboolean` is used for then this should fix this bug and prevent future similar ones.

Here's a failed test with the current version of Cheerio:

    var cheerio = require("cheerio"),
    	$ = cheerio.load('<input type="hidden" />');

    $("input").removeAttr("type"); // Type is now set to false instead of being removed

    var out = $.html(); // This will fail since it thinks type is a string
Changed == to ===
Added test
Fixed test
cheerio: rm unused variable
parse: rm unused variables
Merge pull request #487 from coderaiser/patch-2

parse: removed unused variables
Merge pull request #486 from coderaiser/patch-1

cheerio: rm unused variable
don't test on 0.8, don't ignore 0.11

travis seems to have problems with node 0.8
0.11 should be fixed, though
Merge pull request #481 from AMKohn/patch-1

Fixed a bug in removing type="hidden" attr
Merge pull request #480 from alexeyraspopov/patch-1

add `muted` attr to booleanAttributes
use dom-serializer module
Merge pull request #458 from cheeriojs/renderer_module

move render.js to its own module
Fixed encoding mishaps. Adjusted tests.
Merge pull request #499 from alexindigo/master

Fixed encoding mishaps. Adjusted tests.
Merge pull request #457 from cheeriojs/html_fix

Append new elements for each element in selection