Move toHTML to ui package

toHTML/toText will be Blaze functions.  HTMLjs gets smaller; it's just a syntax library with constructor functions, and any code that consumes HTMLjs trees can decide what objects are legal in it.  Having a version of toHTML that doesn't know about Blaze just seems like extra code right now.
Create blaze-tools package with JS code gen utils

This will be the part of Blaze that is needed at compile time by template compilers like Spacebars.
UI.View wip
Remove unreachable return
Crazy intermediate state where most tests pass

So, now instead of bare closures we use UI.Live for reactivity, which evaluates immediately.  Templates are still evaluated lazily.

Next step is to never evaluate components lazily, only views immediately.

UI.Live in attributes is a little gnarly.

Try disallowing bare closures and see what breaks.

We expect embox to be problematic wrt the current component, without Vars.  Maybe the reason for failing markdown test?

Lots of extra calls to withCurrentParentComponent, of course, which should be currentView anyway.