Implemented functions makeCacheMatrix and cacheSolve.

Functions to create a cached matrix which caches its inverse computed and
the function interface to compute the inverse of a matrix. The auxiliairy
function makeCacheMatrix is used to store the cached value of inverse and
return that as per request. Interface function cacheSolve retrieves the
inverse from the cache and return. If the inverse is not already computed
cacheSolve performs the necessary computation and caches the value before
return the result.