Apply the latest Beman Standard

[neatudarius]

Apply the Beman Standard to Beman.Example and more tweaks.

Issues:

• 14

• 16

• 9

• 8

Updates related to the Beman Standard:

• [x] Update licence
  • [x] Apply LICENSE.APACHE_LLVM: Switch from MIT to Apache License v2.0 with LLVM Exceptions.
  • [x] Apply LICENSE.CRITERIA: already applied
  • [x] Apply LICENSE.APPROVED: already applied
• [x] Apply FILE.COPYRIGHT
• [x] Naming
  • [x] Apply LIBRARY_NAMES:
  • [x] Apply REPOSITORY_NAME: renamed to Example (docs + github)
  • [x] Apply TOPLEVEL.CMAKE: already applied (root CMakeLists.txt, using Ctest)
  • [x] Apply TOPLEVEL.LICENSE: renamed file to LICENCE.
  • [x] Apply TOPLEVEL.README
• [x] README
  • [x] Apply README.TITLE
  • [x] Apply README.PURPOSE
  • [x] Apply README.IMPLEMENTS
• [x] CMake
  • [x] Apply CMAKE.DEFAULT
  • [x] Apply CMAKE.SKIP_TESTS
  • [x] Apply CMAKE.AVOID_PASSTHROUGHS

• [x] Tree

  • [x] Apply DIRECTORY.INTERFACE_HEADERS:

    $ tree include 
    include
    └── Beman
        └── Example
            └── example.hpp

  • [x] Apply DIRECTORY.IMPLEMENTATION_HEADERS: currently N/A

  • [x] Apply DIRECTORY.SOURCES:

    $ tree src 
    src
    └── Beman
        └── Example
            ├── CMakeLists.txt
            ├── example.cpp
            └── tests
                ├── CMakeLists.txt
                └── example.t.cpp
    
    4 directories, 4 files

Updates related to docs and usage example:

• [x] Add API example: beman::example::identity equivalent of std::identity
• [x] Add basic unit test and framework integration with Gtest: src/Beman/Example/tests/example.t.cpp.

  
  $ tree src/Beman/Example/tests 
  src/Beman/Example/tests
  ├── CMakeLists.txt
  └── example.t.cpp

1 directory, 2 files

- [x] Add usage example: `examples/sample_usage.cpp`.
```shell
$ tree examples 
examples
├── CMakeLists.txt
└── sample_usage.cpp

1 directory, 2 files

• [ ] Docs
  • [ ] Add build instructions docs.
  • [ ] Document minimum compiler requirements
  • [ ] Add required tools/packags.
  • [ ] Add OS support.
  • [ ] Add deps support.
  • [ ] Add C++ standard support.

Updates related to CI/infrastructure/other missing bits:

• [x] Extend compiler / standard versions for build and run on CI: {gcc, clang}x {C++98,C++03,C++11,C++14,C++17,C++20, 'C++23, C++26}.
• [x] Add CI Tests badge in root README.md.
• [x] Add .gitignore
• [x] Add .github/CODEOWNERS