implement whitespace removal for Diet templates

[japplegame]

Haml syntax: http://haml.info/docs/yardoc/file.REFERENCE.html#whitespace_removal__and_
and more Jade-like Scalate syntax: http://scalate.fusesource.org/documentation/jade-syntax.html#Whitespace_Removal:__code__gt___code__and__code__lt___code_

I think this is really useful feature.

It is compile time implementation, so removing whitespace inside runtime constructions (like if or foreach) works, but a little weird.

For example:

div<
    - foreach(i; [1, 2, 3])
        img

generates

<div><img/><img/><img/></div>

but not expected

<div><img/>
    <img/>
    <img/></div>

because < removes whitespace before img tag, and foreach repeats it 3 times already without whitespace.

[s-ludwig]

Nice, this would also solve issue #244. I'll make a detailed review later, but (even though it reverses how Jade does things) I like how this approach keeps the HTML output tidy in general. Do you have time to add a short paragraph with some examples in https://github.com/rejectedsoftware/vibed.org/blob/master/views/templates.dt? I would really appreciate that, but if not, I'll allocate some time for that later on.

[japplegame]

By default, Jade inserts indentation everywhere, excluding spans.
Finally Diet is not Jade and IMO It's not necessarily exactly follow all things.

My English is rather bad, but I'll try to add a description.

[s-ludwig]

Hm okay, so now with your changes we could also easily make stripping whitespace around <span> the default.

However, I see it similar, that we don't have to follow everything exactly. And apart from <span>, there can be many other cases, where no whitespace is desirable, for example for a link that is directly followed by a full stop, so I'm for keeping things simple and requiring the >< syntax in all cases (or inline-HTML).

Code looks well btw., will merge.