Feat: colourise default output or add slim output

Currently the output prints the entire file side by side with a `+/-` to indicate changes. On a small screen not only is it confusing seeing `-` which can potentially just be a start of a new item in an list but you end up endlessly scrolling on big files not realising where the changes are. In CI jobs it makes it cumbersome trying to navigate what the actual issue is. The quiet option, which I think is the same as `-output_format line`, only prints the affected file. So its either verbose or absolutely minimal

There are a number of ways i can envisage improvement of output to help end users. I am not very familiar with internals of the library so I am not aware of the simplicity of implementation. I would be happy to contribute changes for something that you identify as low hanging fruit.

Here are some options that come to my mind:
* Adding colour to the output. e.g. red old, green new
* `-output_format` option to only print the affected lines and not the whole file
* Enriching the quiet/line option by pointing out the affected line:character with the type of error/warning. e.g.

I would be happy to contribute if necessary