Style guide for referencing binaries, code artifacts, and env vars

[technosophos]

The text inconsistently uses styles for referencing code-ish artifacts. Sometimes env vars are left unstyled. Sometimes they are stilled. Frequent conventions elsewhere suggest that using a CODE style is appropriate. Similarly, binary names and URLs should have consistent styling.

[bacongobbler]

partially fixed in #11. Some sections like the howto guide and the topic guides need updating.