Generated source is always formatted

[pekim]

Formatting a generated file is nice. However it's causing me a performance problem during development.

I'm generating over 4,000,000 lines, spread over about 200 files, which takes 35 to 40 seconds. Profiling shows that most of this time is in jen. And a large part of the time in jen is spent in formatting the source.

I would like an option to not format the generated source.

[pekim]

Merge request #60 brings my code generation time down to about 12 seconds.

I suspect that the improvement is not all directly related to not formatting. It's quite likely that not formatting is reducing garbage collecting significantly in my use case.