Convert everything to C++

[TimSiebert1]

Hi,

this PR transforms the C sources to C++.

Its not done yet!

[codecov]

Codecov Report

Attention: Patch coverage is 34.71074% with 553 lines in your changes missing coverage. Please review.

Project coverage is 65.56%. Comparing base (3c1f1ed) to head (45af1ab).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
ADOL-C/src/ho_rev.cpp	35.63%	298 Missing ⚠️
ADOL-C/src/uni5_for.cpp	22.67%	133 Missing ⚠️
ADOL-C/src/taping.cpp	50.39%	63 Missing ⚠️
ADOL-C/src/fo_rev.cpp	31.08%	51 Missing ⚠️
ADOL-C/src/adalloc.cpp	30.00%	7 Missing ⚠️
ADOL-C/src/advector.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #92      +/-   ##
==========================================
- Coverage   66.25%   65.56%   -0.69%     
==========================================
  Files          51       51              
  Lines       26686    26239     -447     
  Branches     1843     1848       +5     
==========================================
- Hits        17680    17203     -477     
- Misses       9006     9036      +30     

Flag	Coverage Δ
unittests	65.56% <34.71%> (-0.69%)	⬇️

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