Use a global normalized format that can be converted to any other format

Based on @bertfrees's comment: https://github.com/daisy/pipeline-scripts/issues/101#issuecomment-329759018


These new scripts could use this method:

- EPUB 2 to PEF/BRF script: #136
- MS Word to EPUB 3 script: #135
- MS Word to DAISY 2.02 script: #134
- ODT to EPUB 3 script: #133
- ODT to DAISY 2.02 script: #132
- Markdown to DTBook script: #131
- RTF to DTBook script: #130
- MS Word to DTBook script: #129
- ODT to PEF script: #127
- HTML to DTBook script: #122
- ODT to DTBook script: #121

Start by reading the linked comment in issue #101 and reviewing the related script issues listed here, especially #121–#136. Determine how a global normalized format should support conversion to the requested output formats, and consider that this repository is now part of pipeline-modules. Done means the listed new scripts can use that common conversion approach.

Written by the indexing model from the issue text.