Add formatting, add argument descriptions

Add code formatting tags on element, key, value, method names where missing, from beginning of "Creating Input Elements" up to beginning of "Creating Buttons and Submit Elements";
Add missing examples in the same area of document;
Correct/disambiguate some explanations in the same area of document;
Add the list of arguments with short description right after the method name in each subsection;
Add (where existent) the widget template at beginning of method description to make clear what HTML is output.