Add #clear to reset image to all ‘O’s

- Refactor #initialize to call #clear
Build image clear command
Prevent NoMethodError when no image initialised
Add NoMethodError exception handling

- for #image_clear
Add command for colouring a single pixel
Create vertical strip in image
Missed some clean-up

- call #show
- remove original puts statements (for feedback)
Create horizontal strip in image
Create #colour_area to fill with colour
Refactor to move program to project root

- remove bin directory
- update README adding section on how to run from command line