Let viz(cube, slice=?) plot only one slice of the cube C

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (ea45928) 90.30% compared to head (1d1d1a1) 90.30%.

Files	Patch %	Lines
src/imshow.jl	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1361 +/- ## ========================================== - Coverage 90.30% 90.30% -0.01% ========================================== Files 133 133 Lines 16885 16887 +2 ========================================== + Hits 15248 15249 +1 - Misses 1637 1638 +1 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.