Improve error diagnostics

[alexander-yevsyukov]

This PR makes ProtoData CLI print an exception message caught in the main() function.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 73.91%. Comparing base (2e52d45) to head (8e51f28).
Report is 6 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #355      +/-   ##
============================================
- Coverage     73.95%   73.91%   -0.04%     
  Complexity      618      618              
============================================
  Files           198      198              
  Lines          4311     4313       +2     
  Branches        398      398              
============================================
  Hits           3188     3188              
- Misses          996      998       +2     
  Partials        127      127              

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