[respec] Automatic conversion between WebIDL oldschool and contiguous

Hi,

As alluded before [1], the modern and correct way of writing WebIDL with 
respec is to use the so-called "contiguous" mode rather than the 
"oldschool" one.

As transitioning between the two can require quite a bit of work with 
specs with lots of WebIDL, I've built [2] a respec profile that can help 
(attached).

To use it:
* replace the link to the respec script by a link to that special profile
* save the generated document as the new source for your respec
* re-replace the respec link with the normal respec profile
* fix anchors and auto-links as needed

I have tested this only with one spec so far, and I'm not volunteering 
to maintain and publish that profile much beyond the usage I'll have for 
it in the upcoming few weeks; but I thought I would mention it in case 
others are facing the same conversion needs.

Dom

1. https://lists.w3.org/Archives/Public/spec-prod/2015JulSep/0032.html
2. https://github.com/dontcallmedom/respec/commits/oldschool2contiguous