Linked list implementation done by ruby

#append(value) adds a new node containing value to the end of the list

#prepend(value) adds a new node containing value to the start of the list

#size returns the total number of nodes in the list

#head returns the first node in the list

#tail returns the last node in the list

#at(index) returns the node at the given index

#pop removes the last element from the list

#contains?(value) returns true if the passed in value is in the list and otherwise returns false.

#find(value) returns the index of the node containing value, or nil if not found.

#to_s represent your LinkedList objects as strings

#insert_at(value, index) that inserts a new node with the provided value at the given index.

#remove_at(index) that removes the node at the given index.