Migrate from Dep to Go Modules

Go Modules are the preferred way to manage dependencies in Go programs
since version 1.11. The migration process involves:

 1. go mod init git.dominic-ricottone.com/~dricottone/image2ascii
    (replace the host as needed)
 2. Replace the host in files requiring an internal module
    (this was specifically image2ascii.go, convert/convert.go,
    convert/resize.go, and convert/resize_test.go)
 3. go mod tidy
 4. rm -rf vendor/ Gopkg.lock Gopkg.toml
 5. go get -u

go.mod now contains all the information required to build the program.

Fixed the high cyclomatic complexity issue

update the logic

fixed the lint issue

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