table tests: make guidance less prescriptive (#174)

Handle errors once (#179)

Adds new guidance on how handling errors once
rather than double handling, e.g. log-and-return.

Resolves #65

Add guidance on goroutine lifecycle management (#158)

In general, we prefer for goroutines to have well-managed lifecycles.
No uncontrolled background work that cannot be stopped.
This change tries to distill some of the guidance around it into a style
guide entry.
In particular,

- goroutines must end or be stoppable
- APIs must block for goroutines to finish
- `init()` should never spawn a goroutine