Record segmentation and rollover by size

[justinlittman]

Add support for:

• Splitting long http responses into multiple WARC records using record segmentation. The size of each record is configurable with --record-size.
• Rollover of WARCs by time. The duration of each file is configurable with --rollover-time.

The motivation for these enhancements is to support recording of the Twitter Streaming
API.

[justinlittman]

We've decided to not use record segmentation, so closing this PR.

[nlevitt]

Oh, ok :)