theming attributes

Tumblr uses attributes like this:

{block:JumpPagination length="5"}...{/block:JumpPagination}

But this is rare in Tumblr and we haven't used attributes yet.  I would like to get rid of attributes since they complicate the syntax and the function calls.  In the rare cases where we need attributes, we can do this:

{block:JumpPagination}{block:length}5{/block:length}...{/block:JumpPagination}

or

{define:length-5}{block:length}5{/block:length}{/define:length-5}

{block:JumpPagination}{length-5}...{/block:JumpPagination}

Okay?

I think this is okay for now. We can review this decision if we find harder cases.

done, closing