Added version info.

Now when make is invoked it exec the new script gen_version.sh and generates the file version.h wich contains something like:
```
#ifndef __VERSION_H__
#define __VERSION_H__

#define VERSION_DATE "Sat, 15 Jun 2013 15:15:04 +0200"
#define VERSION_HASH "209a742"
#define VERSION_BRANCH "version_patch"
#define VERSION_REPO "https://github.com/skgsergio/omxplayer.git"

#endif
```
And when omxplayer -v/--version is invoked the result is:
```
root@raspita # omxplayer -v
omxplayer - Commandline multimedia player for the Raspberry Pi
        Build date: Sat, 15 Jun 2013 15:15:04 +0200
        Version   : 209a742 [version_patch]
        Repository: https://github.com/skgsergio/omxplayer.git
```

This should be enough to close huceke/omxplayer#184