Initial commit
Added error handling
Finished chapter 8: S-Expressions
Finished chapter 9 & 10
Squashed 'lib/ptest/' content from commit 7b86d70

git-subtree-dir: lib/ptest
git-subtree-split: 7b86d70da02300590ac2e6467a99aecb09816204
Merge commit '6c6b80ff526b447b748cadf65f1ca6aad38058ea' as 'lib/ptest'
Fixed mod and added test suite