Add Versioning for GhostMem

[el-dockerr]

This pull request introduces versioning support to the GhostMem library, updates the project version to 0.8.0, and surfaces version information both in the build system and at runtime. It also adds corresponding tests to ensure version information is correctly reported.

Versioning support and visibility:

• Added a new header file src/ghostmem/Version.h that defines version constants, version string, and provides helper functions to query the GhostMem version at runtime.
• Updated src/main.cpp to display the GhostMem version string at program startup using the new version helper functions.

Build system and packaging updates:

• Changed project version in CMakeLists.txt from 1.0 to 0.8.0, included Version.h as a header, and set up CMake to define version macros for both static and shared libraries. Also, set shared library version properties for proper packaging. [1] [2]
• Added a new test file tests/test_version.cpp to verify version constants, string, and integer encoding. Registered this test in the build system. [1] [2]

Documentation:

• Updated README.md to prominently display the new version number at the top.