Merge pull request #2 from alistairleak/master

removed gpclib line and removed quotations on sum
updates post tutorial
Merge branch 'master' of https://github.com/Robinlovelace/Creating-maps-in-R
updates intro + structure
major update following feedback from Jan 24th
Sorted more typos and compiled pdf
updated intro, description of square brackets, $ and @ symbols - now just need to rewrite fortify bit.
updates from Rachel added
eval vs echo mistake corrected
removed gpclib line and removed quotations on sum
updates post tutorial
updates intro + structure
major update following feedback from Jan 24th
Test READ ME
Updates and addition of glossary
merging
toc and R quick ref. added
toc and R quick ref. added
Updated aggregate and gIntersects arguments to remove errors
updated pdf