Make headers bold and let termcolor 2.1 determine if colour can be used

[hugovk]

https://github.com/termcolor/termcolor/releases/tag/2.1.0 added support to detect if colour can be used by the terminal, so we can depend on termcolor>2.1 and remove that code from here.

Also make headers bold (when ANSI colour codes available).

Also bump PyPy3.8 to PyPy3.9 on CI.

[codecov[bot]]

Codecov Report

Merging #130 (39eca83) into main (a4e83e6) will decrease coverage by 0.18%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #130      +/-   ##
==========================================
- Coverage   95.40%   95.23%   -0.18%     
==========================================
  Files           9        9              
  Lines         392      378      -14     
==========================================
- Hits          374      360      -14     
  Misses         18       18              

Flag	Coverage Δ
macos-latest	95.23% <100.00%> (-0.18%)	:arrow_down:
ubuntu-latest	95.23% <100.00%> (-0.18%)	:arrow_down:
windows-latest	95.23% <100.00%> (-0.18%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
tests/test_norwegianblue.py	100.00% <ø> (ø)
src/norwegianblue/__init__.py	98.50% <100.00%> (-0.09%)	:arrow_down:

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[adriens]

:clap: Thanks for maintaining your tool, I use it on a daily basis :star_struck: