Misleading behavior for excluded_schemas

[jfinzel]

We expected that the list of excluded_schemas would be based on direct match, but we were surprised when we configured to exclude one schema which is the prefix of another, and both schemas were excluded!

We found this: https://github.com/enova/audit_star/blob/master/audit/audit.go#L276-L284

This should either be based on a direct match, or the docs should be updated to clearly reflect this.