add insert and search
add removal of nodes
add stack structure
raise an exception if Stack is empty
add shippable testing
update README for CI
initial tests
finish binary tree finally
add insertion sort
add a couple tests for insertion sort
clean up insertion sort and test
fix shippaple configuration
refine insertion sort to use ruby's delete & insert
implement merge sort
implement quick sort
test quick sort
Merge branch 'quick_sort'