[vdmkenny]

This is a quality, deduplication and CONTRIBUTING pass over everything merged since 0.20 (#1320 to #1332).

Shared code

• One reader for whole numbers in the mods' manifests: Crew, Tier, and a game variable's Start and Attempt. Its log message names the key and the range it takes, for example "gives Tier the value '5', which isn't a whole number from 0 to 3".
• GameType.playerFlies says whether the player can fly a ship. main.playerShip and the manifests' check both use it, where they used to compare against two different constants.
• layout.isPlaceholder and layout.tagName are now the one home of the rule that a name starting with an underscore is a placeholder. The mission source vocabulary, its reference and definitions writers, the game variables' and ship types' script names, and the scripts' values each spelled it out before.
• gameflow.setFromRecords sets the game's variables for both a new campaign and each attempt.

Tidying

• A family's two base lookups are one optional field, Spec.bases, since a family has both or neither.
• The pause menu's frame, the restart screen's dimmed canvas and its shapes are each worked out once per draw.
• Comments added since 0.20 are rewrapped to 100 columns, and a few sentences in the code and the guides are plainer. A list in the scripting guide no longer splits in two.

The generated references don't change. All tests pass locally.