Add versioning

[MCWertGaming]

Adding versioning to cpp-terminal would allow developers depending on cpp-terminal to depend on a specific version of cpp-terminal and don't have to fear their applications to be broken by breaking changes for example.
This would include using the VERSION variable in cmake and providing a dedicated header cmake will generate and the creation of git tags (like on every pull-request merge).

[MCWertGaming]

Would it be better to provide the version inside something like cpp-terminal/info.h or rather a info.h inside of the root folder to store the project version number. CMake will create a simple macro you can use to something like print the version inside of your application, if you want to do that.

[certik]

You can create cpp-terminal/version.h and fill it with CMake.