Added Group Tabs in NuEdit. First post-1.0 API changes (and some bug fixes).

Also can run NuEdit and play with scripted changes via F# Interactive.

Be mindful the small but important breaking API changes! You will have to adjust your code some!

Changes -

Added group tabs to NuEdit. … 614099b
Renamed World.tryMake to attemptMake to follow the new code standard. BREAKING CHANGE 05825d9
Renamed World.init () to Nu.init (). BREAKING CHANGE 955fcb8
Fixed body physics exception swallowing bug. d3847b5
Improved NuEdit from repl. 1fbd899
Removed ability for '/'s to get into address names. … e44ef74
Fixed bug where Screen.EntityTree was being persisted. bdc59de
EntityTree switch-over bug fix. 9b3f75b