Option return for HtmlElement

Annoyingly ident returns https://github.com/jonathanKingston/wurst/blob/501e8266b8836abb74614dc792c5f7e72141ca94/build/codegen.rs#L273 have to return an Option as we aren't able to return a real result.

The real problem is that the following code returns an option: https://github.com/jonathanKingston/wurst/blob/501e8266b8836abb74614dc792c5f7e72141ca94/build/codegen.rs#L288

Perhaps the code could create and hold ownership of multiple dyn references at create element time?

Start by reading build/codegen.rs at the referenced lines 273 and 288, focusing on how HtmlElement and the optional result are generated. Clarify the ownership and return-value requirements before choosing an approach. Done should ensure HtmlElement generation handles the optional result without requiring an invalid concrete return.

Written by the indexing model from the issue text.