Add a simple reset function

[t-moennich]

We use panini for e-mail development and testing in a i18n multi product environment.

Sometimes panini picked up the wrong partials (same file name, different directories) so we end up with this simple workaround.
Everytime a file was changed, we reset the global panini object and enforce a fresh creation.

As this fixed our issues this may be related to some internal caching issues.
Any other working solution would be appreciated :)