new esc.Run signature requires more template

[TomOnTime]

I recently upgraded to the newest version of this module and I noticed that esc.Run() now requires an io.Writer. That's awesome, however old code requires a lot of template (see StackExchange/dnscontrol#515 for an example).

Would it make sense to have (for example) a nil writer result in the file being created automatically? This would help with migrating old code, and also would reduce the amount of template code needed.

Just a though!

[madelynnblue]

Yes this should be the case.