[mkgmap-dev] option to omit road refs from index

Hi Gerd, please find attached a patch that adds a new option --omit-highway-refs-from-index, that causes labels containing highway shields to be omitted from the address index. Please try and commit if you are happy with it. Note, I am on holiday for the next week, so if it needs any changes, I will look at it when I get back. Regards, Mike