Use the revampled HTML chunking everywhere

The zedai-to-epub3 script was never updated to use the revample
HTML chunking facility from the html-utils, resulting in poor
chunking in dtbook-to-epub3 and zedai-to-epub3.

This fixes part of [issue 309](https://code.google.com/p/daisy-pipeline/issues/detail?id=309)
Merge pull request #21 from daisy-consortium/chunking

Use the revampled HTML chunking everywhere