Add ascii title generation closes #4 (#5)

* [ImgBot] Optimize images

/banner-nyan.png -- 114.47kb -> 64.04kb (44.06%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

* add generated banner

* example in readme

* undo default banner.txt

* font description

* add title test

Co-authored-by: ImgBotApp <ImgBotHelp@gmail.com>

Set go 1.11 as the minimum go version.