Improve status table implementation

[minecrafter]

This pull request improves the status table implementation in a few ways:

• Removes defer calls. Using defer to cover reading or modifying a map is superfluous.
• Change underlying data structure from map[string]bool to a map[string]struct{}, which is more appropriate as this is essentially a thread-safe set.
• Adds testing.

[lunny]

LGTM

[appleboy]

LGTM