Missing formaction attribute

Hello,

I like to get your thoughts about the currently not support formaction
attribute in lynx. Our hope is that it will be supported in lynx.

H. 

## Motivation

Developing web applications that respect also text browsers w/o
javascript support; in particular for accessebility.

## Description

HTML5's button formaction attribute allows for buttons to point to another endpoint different than what main form tag specifies. This way it is possible to avoid having lots of forms for simple actions instead of just one big one, but currently CLI browsers such as lynx, links, elinks, etc ignore this attribute and try to send data wrongly to form's main endpoint.

Example:

```html
<form action="/main_action" method="post">
  <!-- ......... -->
  Item1<button type="submit" formaction="/remove_action?item1">Remove</button>
  Item2<button type="submit" formaction="/remove_action?item2">Remove</button>
  Item3<button type="submit" formaction="/remove_action?item3">Remove</button>
  <!-- ... -->
</form>
```

The above example, buttons should send form data to /remove_action instead of /main_action, the current and only workaround is one form per possible action like:

```html
<form action="/main_action" method="post">
  <!-- ......... -->
</form>
<form action="/remove_action?item1" method="post">Item1<button type="submit">Remove</button></form>
<form action="/remove_action?item2" method="post">Item2<button type="submit">Remove</button></form>
<form action="/remove_action?item3" method="post">Item3<button type="submit">Remove</button></form>
<form>
<!-- ... -->
</form>
```

Which is subobtimal for the application development and hurts performance.

## Specification of Attribute

 * https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#attr-fs-formaction