makeCacheMatrix:  this function creates a vector of functions, which serve to:
    * set the value of a matrix
    * get the value of the matrix
    * set the value of the inverse of the matrix
    * get the value of the inverse of the matrix.

 cachesolve:  Return the inverse of the matrix in the above special vector.  If the inverse
 has been previously calculated and stored, return the cached value of the inverse.
Drop some unnecessary comments