add a draw_ship method in interpreter
rename window -> ctx
draw ship in sdl app
add a move_ship method
refactor run to use a record as ctx
add move_ship logic
display ship in js app
remove move_ship
handle mouse move in JS app
move with keyboard too
Merge branch 'ship'

Closes #19

* ship:
  move with keyboard too
  handle mouse move in JS app
  remove move_ship
  display ship in js app
  add move_ship logic
  refactor run to use a record as ctx
  add a move_ship method
  draw ship in sdl app
  rename window -> ctx
  add a draw_ship method in interpreter