fixed script error

'figures' directory is necessary to make bookgen.rb work
Merge pull request #11 from hirotnk/feature/script_fix

fixed script error
Macneil Shonle and his eagle eyes made some major editorial points, thanks bro
Thanks to Bob Ippolito for his very thorough editing
a concepts
Small corrections to chapter 3, from the upstream.
Merge branch 'master' of git://github.com/coderoshi/little_riak_book into pt