The simplest CMake template for C++

Before, I typically copy the contents of this directory to a project root folder whenever I'm setting up one, and It's going to be tiring to do that after a while. Instead of that, just clone the repo and delete the .git folder afterwards.

Additional info:
- The .gitignore file disallows everything except the ones that are explicitly allowed.
- If you have read the .gitignore file, the following directories are already whitelisted for you:
  - src/
  - include/
  - lib/
  - docs/
  - tools/
- It should also work in C.
- By default, the output directory is located in /out directory, and it's suppose to partially follow the Filesystem Hierarchy Standard (FHS) but only the directories needed in an executable or library. You can change this behavior by tinkering in the CMakeLists.txt