Switch from to branches for configurations

The existing setup with subdirectories lacks the simplicity users want from a fire and forget start project.

https://github.com/fowles/abseil-hello

Switches to a structure where each branch contains *only* the information needed for that build system. Major changes:

* cmake now includes googletest
* cmake and bazel build the same code and tests
* neither includes extra subdirectories
* all the README's have been reworked

Because this requires adding several branches, the ordinary "pull request" workflow doesn't work so I am just pointing to a finished repo for you to pull from.

The issue proposes moving from a subdirectory-based structure to a branch-per-build-system model, referencing a complete example repo. Start by examining the current repository's structure and the linked 'abseil-hello' repo to understand the proposed branch layout. Focus on how CMake and Bazel configurations are separated and how they integrate googletest. 'Done' means the repository has multiple branches (e.g., for CMake, Bazel) each containing only the necessary build files, with updated READMEs.

Escrita pelo modelo de indexação a partir do texto da issue.