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.

deps/deps.go

@@ -14,7 +14,7 @@ import (
 )
 
 // Deps holds dependencies used by many.
-// There will be normally be only one instance of deps in play
+// There will be normally only one instance of deps in play
 // at a given time, i.e. one per Site built.
 type Deps struct {
 	// The logger to use.
@@ -55,10 +55,12 @@ type ResourceProvider interface {
 	Clone(deps *Deps) error
 }
 
+// TemplateHandler returns the used tpl.TemplateFinder as tpl.TemplateHandler.
 func (d *Deps) TemplateHandler() tpl.TemplateHandler {
 	return d.Tmpl.(tpl.TemplateHandler)
 }
 
+// LoadResources loads translations and templates.
 func (d *Deps) LoadResources() error {
 	// Note that the translations need to be loaded before the templates.
 	if err := d.translationProvider.Update(d); err != nil {
@@ -76,6 +78,9 @@ func (d *Deps) LoadResources() error {
 	return nil
 }
 
+// New initializes a Dep struct.
+// Defaults are set for nil values,
+// but TemplateProvider, TranslationProvider and Language are always required.
 func New(cfg DepsCfg) (*Deps, error) {
 	var (
 		logger = cfg.Logger