Improve binary file added output

[Sondeyy]

Targeting: #96

If the binary file changed, it will output the Binary files a/foo and b/foo differ as before.
If the binary file got added or deleted, it will append (binary file) to the filename, print the diff header and skip the body.

Tests:

• binary file added
• binary file removed
• binary file changed

[dandavison]

LGTM! Thanks very much for this work. (I tested it manually using #96 (comment))