Add minimal package file defining \Rcall

\Rcall is used to write calls to R commands in LaTeX files. The
LaTeX code is simple: it looks up the macro's argument in an array
and returns ? if there's nothing in the array for that key.

The commit also adds an example .tex file to illustrate the code.
Write R script to extract code from LaTeX file

This commit writes a basic R script that uses knitr to pull out
any code in the lstlisting environment and also pulls out and
evaluates any code listed in \Rcall.
Change capitalization in LitLR
Bump version and update NEWS file