add monomial
add solve for k
move to functions to files
add monomial interpolate function
finish up cubic spline
add part a,b,c
add newton
add newton diff
Merge branch 'probset/item_4'

* probset/item_4:
  add newton diff
  add newton
  add part a,b,c
  finish up cubic spline
  add monomial interpolate function
  move to functions to files
  add solve for k
  add monomial