updates after smsim course

Hi Robin,

I made so many changes to CakeMap.R that I decided to make a new directory with my code in it. See fractional_weights. This avoids the integerisation and produces a long form table with n individuals replicated over z zones but with the fractional weights attached - so no replication.

ymmv as they say!

I've also included my notes which you may/not want to merge to your master.

thanks again for a great course - it saved me about 6 months of struggle!

PS who won the book? :-)