Some improvements

[mazzucode]

I think this plugin is awesome! I made some improvements, i hope it can be useful. Some notes about them:

• Better readability (Mainly 'ungle Bob' tips)
• Fixed bug that doesn't remove expired cache files
• Better parameters validation
• Now it creates the cache folder if it doesn't exist
• Use of getenv() instead of $_SERVER

[dead23angel]

@masimao thanks!