Add postinstall/update hooks.
More command polish.
Move haxelib.json to the src dir to avoid redundant params in dev mode.
Add `flambe update`.

I'd prefer to have all updating happen over npm, but unfortunately the
npm post-install/update script runs as an underprivileged user. We need
it to run at the level of the current user to install the flambe
haxelib. Ah well.
Even more command polish.