Custom test, ANY_of_exprs(...), and misc fixes.

Added custom test, ANY_of_exprs(...), to Missing Values lesson. 
* Returns TRUE if e$expr matches any of the expressions given (as characters).
* Applied as ANY_of_exprs('x*3', '3*x')

Updated lesson types to Coursera. 
Updated versions to 2.2.0. 
Filled in one author field.