Add possibility to have non void self closing HTML tags

[V4ldum]

resolves #44

I added a parameter to enable/disable the feature. It is false by default but I can make it true.
Please tell me if I missed or should improve some things !

[bram209]

Hi, thank you for your contribution!

I would like to do this slightly differently. When I created the formatter, leptos was still using syn-rsx for it's html-like syntax. The problem with syn-rsx is that it would not capture the closing tags in its AST.

However, as the author of syn-rsx has unfortunately passed away, leptos is now using its improved fork rstml.
This new fork does capture closing tags, so now it is possible to preserve the original closing tags by default.

I propose to add a configuration option named preserve_void_element_closing_tag that is by default set to false.
Keep in mind that this goes directly against the HTML specification:

A void element is an element in HTML that cannot have any child nodes (i.e., nested elements or text nodes). Void elements only have a start tag; end tags must not be specified for void elements.

In HTML, a void element must not have an end tag. For example, <input type="text"></input> is invalid HTML.

[bram209]

Ah wait, this is about non void elements... in that case the current approach is fine, except that I would like to preserve the closing tag (self-closing or not) based on the source. With the current PR it will format <div></div> to <div />.

Let's add the following option:

/// Preferred style for closing tags (self-closing or not) when a non-void element has no children
closing_tag_style: ClosingTagStyle

// ...

enum ClosingTagStyle {
  /// Preserve the original closing tag style (self-closing or a separate closing tag)
  Preserve,
  /// Self closing tag for elements with no children: `<div></div>` formats to `<div />`
  SelfClosing,
  /// Separate closing tag for elements with no children: `<div />` formats to `<div></div>`
  NonSelfClosing,
}

[V4ldum]

I think I fixed all the issues reported (except the macro, cf the discussion on that topic). I took the liberty to add some tests for the non closing style too, but commented those out while the macro topic is not resolved

[V4ldum]

Everything should be good now, thank you very much for the feedback !