Fix most linter warnings reported by 'staticcheck'. This doesn't fix all
of them, some unused functions are still there, and some generated code
also still triggers some warnings. Most issues are fixed, though.
No functional changes, except for the captialisation of some error
messages.
This is a better way to check errors, both semantically (no usually nil is
bad, but nil error is good, so this avoids a mental negation) and for
the reporting by the assert package.
This is not yet working, it's just a direct copy of the Manager of Flamenco
2, with Logrus replaced by Zerolog. The API has been documented in
flamenco-manager.yaml as a starting point for the integration.
