Add --verbose flag

[sermuns]

It seems to be hard to both get a streaming output to your terminal AND capture the stdout of the running command.

This is a PoC, it just shows the invoked command and prints the captured output to the terminal. Might wanna show WHAT block in the markdown file it originated from.

Fixes #35.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.76%. Comparing base (a28dabd) to head (88af2c6).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/command.rs	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #36      +/-   ##
==========================================
- Coverage   95.12%   94.76%   -0.37%     
==========================================
  Files          12       12              
  Lines         431      439       +8     
==========================================
+ Hits          410      416       +6     
- Misses         21       23       +2     

Flag	Coverage Δ
unit	94.76% <87.50%> (-0.37%)	⬇️

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