TODO:
/**
* Smarty plugin: meta
* Allow binding post or page metada to a template
*
* @param {array} $params
* $params['post_id'] ID of the post or page
* $params['meta_key']
* $params['meta_value']
* $params['meta_single']
* $params['default']
* $params['type'] (optional) If is it set to 'object' it will return an object, otherwise it will return a JSON string.
* $params['assign_to'] Variable withing the template engine to which the content has to be assinged.
*
*
* @example
*
* # EXAMPLE 1
* {meta post_id="25" assign_to="my_meta"}
* <p>My favorite color is {if $my_meta.data.color}$my_meta.data.color{else}UNKNOWN{/if}</p>
*
* # EXAMPLE 2
* {meta post_id="25" meta_key="color" assign_to="my_meta"}
* <p>My favorite color is {if $my_meta.data.color}$my_meta.data.color{else}UNKNOWN{/if}</p>
*
*
* @see http://www.smarty.net/docs/en/plugins.functions.tpl
*
*/