Refactor the code to match the oop mode for easy mock and test

add the fit options to scale the image to fit the screen

refactor the convert package

Rewrite the go docs

fixed the comment

fixed the resize.go code style issue

remove the useless code

Add the method to fit the screen

add some depedencies to calc the terminal size

change the char width to 0.5

remove some useless code

add the resize package