Fix rendering of code block

Also add $ to tell input from output
1. Adding `helper` field to header (like `instructor` field).
2. Updating `README.md` to explain what it's for.
3. Updating index page validator to check `helper` field.
Addressing comments by @r-gaia-cs
Adding back the glossary checker
Making placeholders for missing glossary entries
Removing parable about startups and education: snarky, and not really informative
Tidying up bib entries
Reformatting bibliography
Converting to individual challenge div's in the novice shell lessons
Converting to single-div-per-challenge in novice Git tutorial
Explaining that argument vs. parameter is inconsistent
Cleaning up glossary definitions of argument and parameter
Merge pull request #506 from gvwilson/adding-helpers-to-home-page

Adding helper field to home page template.
Merge pull request #515 from gvwilson/putting-books-before-papers

Putting books before papers
Merge pull request #516 from gvwilson/removing-parable-about-startups

Removing parable about startups and education
Filling in missing glossary entries
Regularizing case in glossary definitions
Merge pull request #512 from gvwilson/checking-glossary

Checking glossary
Command-line merge of updates to glossary
Bugfix: code block not rendering in 02-func