Scripts for packaging Linux release

Added a script for generating a release tarball for Linux systems, ready to be redistributed.
The package generated is a stand alone and should run on systems where SFML is not installed.

The tarball will contain:
- Executable and assets
- SFML .so files
- A shell launcher

The launcher adds the SFML .so files to the LD_LIBRARY_PATH and then invokes the executable.

Usage:
```
$ ./tools/linux-release.sh 
Enter version number: 0.5.2
Packaging kroniax_0.5.2-linux.tar.gz...
Done!
```

Currently the script looks for SFML .so files only in `/usr/local/lib`, so this point could be improved.