Helpers should be static

[davidmosterd]

After reading: "It makes it obvious to users how the class is used" as an argument on static classes I think the helpers ought to be static.

It would rid us of the ac_helper() function and clean the syntax a little. Also, they don't allow a constructor and have no properties. It's not going to happen.

Should it happen; then the accessor ac_helper() should at least be removed as it couples behaviour of helpers very tightly. If you would want to write a Column Helper ever, which would benefit from an AC_Column object that would not be possible now.

AC_Helper_String::function
ac_helper()->string->function

We might even consider adding global scope function since those are helpers in general and there is no coherence between many functions.

ac_str_word_count()
ac_array_key_replace()