Add support for \ensuremath{...}

[Delivers #63077604]
Issue pull request for branch 63077604-ensuremath

[Delivers #63077604](https://www.pivotaltracker.com/story/show/63077604)
Properly prepend the fontsize in PDF books

[#63083948]
Issue pull request for branch 63083948-pdf-source-code
Merge pull request #96 from softcover/63083948-pdf-source-code

63083948 pdf source code