Change test runner to pytest

[Paebbels]

• [x] Bump version to v0.6.2 v0.6.3
• [x] Updated file headers to 2021.
• [x] Updated PyCharm project files.
• [x] Update setup.py.
• [x] Update conf.py.
• [ ] Add dependencies.
• [x] Change test runner to pytest

[codecov[bot]]

Codecov Report

Merging #14 (72b299a) into master (e4abe1f) will decrease coverage by 1.99%. The diff coverage is 53.52%.

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
- Coverage   44.04%   42.04%   -2.00%     
==========================================
  Files          83       76       -7     
  Lines       11087    10562     -525     
  Branches     2120     2017     -103     
==========================================
- Hits         4883     4441     -442     
+ Misses       5911     5860      -51     
+ Partials      293      261      -32     

Flag	Coverage Δ
unittests	42.04% <53.52%> (-2.00%)	:arrow_down:

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

Impacted Files	Coverage Δ
pyVHDLParser/Base.py	91.66% <ø> (-8.34%)	:arrow_down:
pyVHDLParser/Blocks/Common.py	61.76% <ø> (ø)
pyVHDLParser/Blocks/ControlStructure/Case.py	24.03% <ø> (ø)
pyVHDLParser/Blocks/ControlStructure/Exit.py	17.04% <ø> (ø)
pyVHDLParser/Blocks/ControlStructure/ForLoop.py	26.01% <ø> (ø)
pyVHDLParser/Blocks/ControlStructure/If.py	25.76% <ø> (ø)
pyVHDLParser/Blocks/ControlStructure/Next.py	17.04% <ø> (ø)
pyVHDLParser/Blocks/ControlStructure/Null.py	33.33% <ø> (ø)
pyVHDLParser/Blocks/ControlStructure/Return.py	26.92% <ø> (ø)
pyVHDLParser/Blocks/Expression.py	11.88% <ø> (ø)
... and 67 more

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