Note: please be aware that this is an approximate amount. It IS possible
that this is not the exact amount of search results,
since search results may vary in time (entries may not yet/no longer be
shown) and we will not rebuild the entire search index
on every search (would be a great performance killer and huge scalability
loss)
This function can be called with either a string as parameter (simple
search) or an array (advanced search)
Simple search: all search index fields will be searched for the given
term
Advanced search: only the given fields (keys in the array) will be
matched to the corresponding values (corresponding values in the array)