booleanAttr for components

[zkat]

Components that want to use HTML-style booleans are currently forced to write this function manually. I think this is valuable enough to can.Component users that it's good to have built-in to the define plugin.

[zkat]

Alternately, we might call this "htmlbool" or similar. Say the word and I'll push a fix.

[wclr]

How this is supposed to be used, elaborate, please.

[zkat]

In HTML, boolean attributes are provided by simply writing the name of the attribute itself without a "value":

<script async>...</script>

In this example, async would be interpreted as true by the <script> tag. The attribute's absence implies it's false. See http://www.w3.org/TR/html4/intro/sgmltut.html#h-3.3.4.2

[wclr]

Yes I think this is needed, maybe even add feature like no- prefix to such attributes that will negate the value `and``

[daffl]

Looks good. Do we need to add a test for this though?

[justinbmeyer]

And docs.

[zkat]

@daffl done