Ebookmaker

- add a minimal css stylesheet to the html generated for txt files
- delint

- added rendering for <q>: ebookmaker will now change all <q> tags to <span> for epub builds, keeping any attributes on the tags. curly quotes will be added inside the spans, double for top level q and single for all q nest in other qs.

- corrected text in PG footer for RST - thanks Roger Frank. Note that boilerplate generation is being revised for v0.11
- when reflowing pre, don't make it one long line. This was causing problems in the Kobo reader.
- don't drop a heading that starts with "by " if class 'x-ebookmaker-important' is on it.
- also log headings that are dropped because they start with "by "
- fix bug in anchor fixing where if an <a> tag had both id and name attributes, both were deleted.
- delinting

- fixed minor issue where "too deep" errors were emitted for self-links. Thanks to rfrank for the error report.
- fixed deprecation warning from Docutils; should be ok for Docutils > 0.1

- SVG files are now considered images and included in EPUBs. They were being discarded. SVG files are not scaled or compressed by ebookmaker - the renderer should be able to auto-scale. This appears to fix kindlegen failures associated with svg images.
- fixed the rst test

- changed font for rst conversion. Linux Libertine was unmaintained since 2012 and no package was available for CENTOS8. We switched to the closest replacement, Libertinus https://github.com/alerque/libertinus
- added documentation about configuration for rst conversion
- the deprecated 'handheld' media query was being used to prevent ebookmaker from stripping floats. to preserve this feature, ebookmaker no longer strips floats when the css selector contains the x-ebookmaker class. Most likely, float stripping was originally needed because html pages were designed before the advent of EPUB. Today, we can assume that if the html designer uses the x-ebookmaker class, they've considered the impact of the float on the generated EPUB.
- assorted delinting