This Function allows it to highlight assigned Parts (needle) of a string (hystack) with pre defined HTML-Tags by only once call of function. Surely, in PHP4 it would be much
easier to realise such a function - but this function works in PHP3, too. To define the tags that highlight the needle in the hystack-string use an array consisting of two
values  (for opening the tag(s)) and  (for closing the tag(s)). The function doesn't do any echo's, it only returns the value, so you have to call it in order with echo to
write what it returns.