Update code style

Normalize usage of spaces and semicolons.
Manage context explicitly

Instead of passing the context as a required first argument, manage it
using JavaScript's `Function#call` facilities. This makes private
functions easier to read and maintain.
Fix bug in setting styles

When setting the style of a multi-element selection, ensure that each
style is set independently.
Implement API for unsetting styles
Implement API for getting multiple styles
Implement API for setting styles with a function
Remove undocumented functionality

The 0-argument signature is not supported by jQuery's `css` method.
Document 'css' method
Remove dead code path

This condition is never satisfied because the private `parse` function
never returns `undefined` or `null`.
Merge pull request #272 from jugglinmike/fix-css

Improve `css` method