Allow for Buffer charts to be tested in CLI mode

[FranjoMindek]

Currently it's easy to test ImageCharts charts in CLI mode since they are hosted on their own server.
While we can easily send Buffer as a file attachment to Discord, we can't do the same for the CLI.

For now I see these approaches:

1. Save the Buffer chart as a image in the os.tmpdir(), provide the file path to user in CLI
2. Use library which allows us to display pictures in terminals (might not work on all terminals)
3. Use library which allows us to transform pictures to ASCII alternatives

[Martinsos]

Makes sense! I wouldn't do (3) because then we are not testing much :D, but (1) or (2) make sense. Probably (1) is the best solution, well depends how widely is (2) supported.