Delete only unneeded PolyTeX files

[#61839564]
Cache the digest of Markdown files

[Delivers #61839564]
Issue pull request for branch profile-61839564

[Delivers #61839564](https://www.pivotaltracker.com/story/show/61839564)
[Delivers #62358298](https://www.pivotaltracker.com/story/show/62358298)
[Delivers #62423444](https://www.pivotaltracker.com/story/show/62423444)
[Delivers #62349942](https://www.pivotaltracker.com/story/show/62349942)
[Delivers #62182392](https://www.pivotaltracker.com/story/show/62182392)
[Delivers #62094332](https://www.pivotaltracker.com/story/show/62094332)
[Delivers #62114976](https://www.pivotaltracker.com/story/show/62114976)
Issue pull request for branch profile-61839564
Change to use tmp/ for cache since it's already gitignored

[#61839564]
Merge pull request #79 from softcover/profile-61839564

Profile 61839564