Add 'single quoted strings'

[eugenesvk]

Currently only "double-quoted strings" are recognized with the scope name of string.quoted.double.ahk, but not
'single quoted strings'.
I've created a patch via a simple copy&paste of this scope but for single quote marks also changing the name to string.quoted.double.ahk and removing constant.character.escape.ahk, which as far as I understand is not needed for single quoted strings