improve and cleanup template helper documentation

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes 
| Applies to    | all
| Fixed tickets | 

This documentation was quite limited before, added all the parameters and explain them. Rather than having a copy of the same doc once with ``$`` and once without, i chose to put them together. There is a minimal loss in readability but a great reduction of redundancy (which by the way already let to diverging doc for a couple of methods).