Add a cover? conditional

[#69782146]
changed the cover images
Update gitignore
Merge branch 'master' of https://github.com/softcover/softcover
include full html in publish

* allow local book directory config file override
* version bump
Add MathJax to single-page output

[Delivers #60244750]
[#60244750]

* 60244750-mathjax-single-page:
  Add MathJax to single-page output
Merge branch 'master' into full-page
Merge branch 'full-page'
Merge branch 'master' into 69782146-cover-options
Switch to JP(E)G by default

[Delivers #69782146]
[#69782146]

* 69782146-cover-options:
  Switch to JP(E)G by default
  Add a cover? conditional
Bump version number