docs: Add missing docstrings, adjust wording to match standard style

This patch adds a missing docstrings for exported identifiers, and
adjust some of the existing ones to match the standard style.

In some cases, the identifiers were un-exported after noticing they had
no external users.

Besides improving documentation, it also reduces the linter noise
significantly.

internal/config/config.go

@@ -81,6 +81,7 @@ func Load(path string) (*Config, error) {
 	return c, nil
 }
 
+// LogConfig logs the given configuration, in a human-friendly way.
 func LogConfig(c *Config) {
 	log.Infof("Configuration:")
 	log.Infof("  Hostname: %q", c.Hostname)