Basic move to Catch2 3+

[Arniiiii]

Fixes: #47

[loqs]

Following on from the basic move all instances of the combined header catch2/catch_all.hpp can be replaced bycatch2/catch_test_macros.hpp with the following needing catch2/matchers/catch_matchers_floating_point.hpp for the WithinAbs matcher:

• test/transducer/range.cpp
• test/transducer/unzip.cpp
• test/transducer/zip.cpp
  Additionally the CATCH_CONFIG_MAIN define can be dropped from test/CMakeLists.txt and test/__inline_var_tests/main.cpp as Catch2::Catch2WithMain provides main().