Ebookconverter

- fix bad error handling in FileInfo
- don't save new credit unless it's new
- libgutenberg 0.10.22
- fixes bugs that resulted in duplicate credits
- fixes a problem that scraped credits overwrote the changes from json file

- credits should be changed, not appended. Fixes 35.
- added a script to remove extraneous credits
- Ebookmaker 0.12.40, libgutenberg 0.10.20

- fix RDFWriter to include the DCMIType ('Text') for books. It does not appear that this ever was done since the advent of EbookConverter. Fixes 42.
- Ebookmaker 0.12.37

- removed the `.utf8` extension from txt, html, and rst generated files

- Removed a txt exclusion. Ebookmaker is now putting headers on txt files, but this was not being done for the 20,000 or so books with source named 99999-0.txt due to the obsolete exclusion.
- add a script that packages txt files to a tarball
- add an HTMLWriter that extends Ebookmaker's HTMLWriter to package up a zip file of the html5 with images named pg99999-h.zip Addresses 38
- don't require a sourcefile for products that are built from the database. Require ebookmaker>0.12.35. Fixes 39.
- save credit metadata to the database. fixes 28.
- corrected behavior of source file size limits
- add ebook number to log even if the source file fails to parse

- adds MastodonWriter, to replicate TwitterWriter (posting on gutenberg_newmastodon.social)