Updated R basics

Addressed all comments raised by Gavin and John on this section. I moved individual items to issues which you can see here:

https://github.com/karthik/bc/issues?state=open
Signed-off-by: Karthik Ram <karthik.ram@gmail.com>
Removed extra file

Signed-off-by: Karthik Ram <karthik.ram@gmail.com>
Updated material on functions

Everything is now converted to Rmd from md.

Signed-off-by: Karthik Ram <karthik.ram@gmail.com>
Updated section on data manipulation

Now all sections are executable code blocks

Signed-off-by: Karthik Ram <karthik.ram@gmail.com>
Added all data files

Signed-off-by: Karthik Ram <karthik.ram@gmail.com>