Add support for color output

[awvwgk]

• color output is controlled by protected derived type instance (no change in calling interface)
• uninitialized color output results in no color
• color output can be triggered on the user side by calling initializer (can be called multiple times)

Closes #13
Closes #12

[codecov]

Codecov Report

Attention: Patch coverage is 71.64179% with 19 lines in your changes missing coverage. Please review.

Project coverage is 69.02%. Comparing base (a78870c) to head (8188210).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/testdrive.F90	71.64%	1 Missing and 18 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #43      +/-   ##
==========================================
- Coverage   71.51%   69.02%   -2.50%     
==========================================
  Files           2        2              
  Lines         481      594     +113     
  Branches      296      296              
==========================================
+ Hits          344      410      +66     
- Misses         23       29       +6     
- Partials      114      155      +41     

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[awvwgk]

Example output:

[jvdp1]

LGTM! I tested it in my different projects, and it works as expected. Thank you.