Improved release downgrade support and bug fixes

• Create RELEASES file and include in tarball so downgrade to initial works
• Support upgrade and downgrade between versions and proper error codes in extended start script (thanks @RJ!)
• Add -p for setting code paths
• Do not write default empty sys.config or vm.args if it exists already from templates
• Add lib_dirs option to for config file, same as -l cli argument
• Fix bug where type none for application in relx config file is not added to the rel file
• Ensure a beam exists for each module defined in an application's .app file
• Fix bug in override resolution
• Add -v/--version cli option