Merges two attribute hashes. This is the same as `to.merge!(from)`, except that it merges id, class, and data attributes. ids are concatenated with `"_"`, and classes are concatenated with `" "`. data hashes are simply merged. Destructively modifies `to`. @param to [{String => String,Hash}] The attribute hash to merge into @param from [{String => Object}] The attribute hash to merge from @return [{String => String,Hash}] `to`, after being merged