Fix some immediate/retained mode confusion
Fix some immediate/retained mode confusion

For future reference:

- Immediate mode = define the tree we want to render
- Retained mode = mutate the tree to what we want it to be

Also, I cleaned up the language a bit.

impinball/mithril.js,pygy/mithril.js,pygy/mithril.js,tivac/mithril.js,lhorie/mithril.js,barneycarroll/mithril.js,barneycarroll/mithril.js,MithrilJS/mithril.js,impinball/mithril.js,MithrilJS/mithril.js,tivac/mithril.js,lhorie/mithril.js