Schema for BuildSteam bst/conf files

[Jim MacArthur <jim macarthur codethink co uk>]

Hi all. I ran into some interesting problems when I wrote my first 
BuildStream project and put this in project.conf:

    name: BSD Games

BuildStream seems fine with a project name which has a space in it, but 
OSTree has a problem with using this as a reference name. Even OSTree 
doesn't make it obvious in their documentation. I had to go to the 
source to find the regexp, "[\\w\\d][-._\\w\\d]*".

Do we want to formally define what fields in BuildStream configuration 
and element files contain? This wouldn't remove the need to put an 
informal description in the documentation, which I'm happy to do after 
the current documentation patches land. If we do think it's a good idea, 
I'd like to suggest using pykwalify 
(https://github.com/Grokzen/pykwalify) to do it, mainly because I've 
used it before, but please suggest other methods. It can be an entirely 
separate script in contrib to start with.

Jim MacArthur