Display actual output on mismatch

[mbrodala]

Right now the only indicator about a output mismatch is a different coloring of the check line (red instead of green) and a global failure status code. It is impossible to see what output was received.

It would be useful to have an (CLI) option to render the actually retrieved output to see what went wrong.

(Notice that a a diff (e.g. using https://packagist.org/packages/sebastian/diff) would be even nicer but this will be a lot harder given that Cigar does not perform a whole string match but actually a substring search.)