Added additional configuration options, enabled compression for MySQL dumps

[mrcasual]

1. File_name format option in config.php
2. compress option for automatic compression of MySQL dump in config.php
3. Optional --compress and --uncompress options for MySQL dumps in Artisan CLI

[schickling]

Thanks for the PR but please also provide testcases for the new feature.

Another thing: I'm not sure whether it would be better to use an extra step to compress the output files. It would also work for other databases. Something like this: http://stackoverflow.com/questions/6073397/how-do-you-create-a-gz-file-using-php