add convert test case

add scale image example

add scale image test cases

add convert package testdata

refactor the convert package

Fixed a slice allocate issue

Rewrite the go docs

fixed the comment

fixed the resize.go code style issue

add colored the asicc output

remove the useless code

Add the method to fit the screen

add some depedencies to calc the terminal size

add new method to convert a image from filename directly

add convert package to convert a image to ascii matrix