Add some missing doc comments

As pointed out by the linter, some exported functions and types are
missing doc comments.
The linter warnings have been reduced from 194 to 116.
Not all missing comments have been added in this commit though.

docshelper/docs.go

@@ -19,14 +19,19 @@ import (
 	"encoding/json"
 )
 
+// DocProviders contains all DocProviders added to the system.
 var DocProviders = make(map[string]DocProvider)
 
+// AddDocProvider adds or updates the DocProvider for a given name.
 func AddDocProvider(name string, provider DocProvider) {
 	DocProviders[name] = provider
 }
 
+// DocProvider is used to save arbitrary JSON data
+// used for the generation of the documentation.
 type DocProvider func() map[string]interface{}
 
+// MarshalJSON returns a JSON representation of the DocProvider.
 func (d DocProvider) MarshalJSON() ([]byte, error) {
 	return json.MarshalIndent(d(), "", "  ")
 }