Adjusts the image size according to the size of the terminal

* There is some confusion about the 'os.popen' module: instead says that it is deprecated, in another the opposite, but I decided to use it:
    - https://docs.python.org/2.7/library/os.html
    - https://docs.python.org/3.2/library/os.html

* README.md:
    - Remove informations (about size) from the README.md
    - Remove tabs from the README.md
    - Adds syntax highlighting