Improve ./makesure -l output

[xonixx]

For Makesurefile

@goal aaa
@doc some description

@goal other_goal
@doc do something important

@goal yet_another_goal
@doc do something even more important

@goal hello

./makesure -l should show

Available goals:
  aaa              : some description
  other_goal       : do something important
  yet_another_goal : do something even more important
  hello