Updated presets.php to use wp_get_themes since get_themes is deprecated starting in 3.4

Note: in 3.4, the way WordPress organizes themes changed. Themes are now keyed by theme slug (stylesheet) rather than by theme name (title).

As a result, there's a bit of duplication / normalizing of theme data to ensure back compatability pre 3.4.

Internally, presets.php always expects, and always returns data keyed to theme slug, and translates it internally for pre-3.4 functions as needed.
documented how to pass callbacks and other arguments to the script in readme.txt and readme.md, fixes #164
Merge pull request #172 from benbalter/wp-get-themes-patch

Update presets.php to use wp_get_themes since get_themes is deprecated starting in 3.4
pass callback as 2nd argument, fixes #174
Cleaner way to pass the callback as a 2nd argument. This way does not require sanitizing the data a 2nd time, and rather relies on the already `json_encode`'d infinite_scroll object.
add package.json
Allow overriding `loading.msg` in the options.
Fixes mixed tabs and spaces and replaces with 4 spaces
Merge pull request #193 from lucisferre/fix-mixed-tabs-and-spaces

Fixes mixed tabs and spaces and replaces with 4 spaces
replaced the $ shortcut by the global jQuery object, in order to support noconflict mode
Merge pull request #195 from shao197/master

Replaced the $ shortcut in behaviors/local.js by the jQuery global object
Merge pull request #188 from aaronjensen/patch-1

Allow overriding `loading.msg` in the options.
Manual triggering: Hide navSelector when end of content reached
Update jquery.infinitescroll.js

The code was not using the option pixelsFromNavToBottom to let me set manually.
Issue #231 - Updated _debug() to handle IE8/9 logging without bombing out
Merge pull request #225 from edirpedro/patch-1

Fixing overwriting of `pixelsFromNavToBottom` option.
Added pathParseOnce option : when set to true, allows to call _determinePath() each time retrieve() is called.
Useful to be able to modify another parameter than the page number in the URL that will be used to load next items.
Also modified Readme.
JSHint fixes.
Issue #238 Fixed _debug() to respect user's debug option.
Issue #223 Changed the loading GIF URL to a data URI.