#225 Update to latest tensor library

[Ulf Lorenz]

The underlying tensor library has been upgrade to use CMake and generally handle dependencies in a better way. In particular, it should now compile with reasonable effort using MSVC under Windows.

TODO

• use CMake native methods to find the tensor library (find_package) and the other dependencies
• make Wavepacket compile with the CMake branch of the tensor library; as long as version 1.0 is not out, maybe we should use a fixed revision.
• optionally, change some of the semantics, for example integers for indices and size_t for sizes; this could be (/already is) a follow-up issue
• take over some of the functionality of the tensor library; ugrade required CMake version
  • calling doxygen directly from CMake
  • using markdown in doxygen using "awesome" theme
  • using clang-tidy in scripting

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• altogether, better interface, worked quite well
• current state of tensor library has a few defects or issues that need to be worked around, but nothing serious