replaced file chooser, improved POD, improved test

Please see the new Changes file for details:
- added Changes file
- removed revision control version number stuff
- removed print command for arguments
- user base instead of direct use of @ISA
- moved POD inside the code, documenting all methods
- extended documentation
- switched from Tk::FileSelect to getOpenFile
- removed requires and added it with use pragma (if you are going to use this module, then you are going to use the dependencies as well)
- removed known bug POD related to FileSelect issue - it's not used anymore
- extended fileentry.t