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

fixed the lint issue

add the mock terminal

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

Add some comments

Add ScaleImage and Image2ASCII benchmark

fixed test

add convert test case

add scale image example

add scale image test cases