Index filtering combo box

Hi @hegemonic,

Although we think having the index in a flat list is better than having a tree component or something like that, when you have very large code-bases it's useful to be able to filter the number of classes down by package. By using a combo-box we get search-based filtering of the packages displayed at any time. The current filter is stored within session storage so it isn't lost as the user navigates the documentation, but by using session storage it doesn't persist into new tabs or windows that the developer opens.

We use a text input box paired with a native HTML5 data-list, so there is no requirement to download a large JavaScript library to use the filter, but where the filter degrades gracefully to a plain text input box on older browsers like IE8 and IE9.

Please let me know what you think?