Initial commit
first rnw commit
keep pdf
class and generics/methods intro
first methods
[.MArray done
validity
replacement methods
introspection
cleaning
misc small text improvements
more cleaning up
updated REDME.md
add S4-tutorial section
text clarifications
more improvements/clarifications
Add '_S4-tutorial/' from commit '63765018b2b4d1e2f936d0de4e1cee79f361f91e'

git-subtree-dir: _S4-tutorial
git-subtree-mainline: 50de16dfac7567826e30662fd579886a73968ba4
git-subtree-split: 63765018b2b4d1e2f936d0de4e1cee79f361f91e