Expand imshow to also call grdview if -p is given

[joa-quim]

No description provided.

[codecov-io]

Codecov Report

Merging #296 into master will decrease coverage by 0.47%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #296      +/-   ##
==========================================
- Coverage   93.87%   93.39%   -0.48%     
==========================================
  Files          80       80              
  Lines        3656     3665       +9     
==========================================
- Hits         3432     3423       -9     
- Misses        224      242      +18

Impacted Files	Coverage Δ
src/psbasemap.jl	100% <ø> (ø)	⬆️
src/gmt_main.jl	78.65% <ø> (-2.38%)	⬇️
src/common_options.jl	95.9% <100%> (+0.01%)	⬆️
src/imshow.jl	95.83% <100%> (+0.83%)	⬆️
src/grdview.jl	97.22% <100%> (ø)	⬆️

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