./bin contains servers for amber-dev as well as webapp-dev.

The `bin/server` installed by npm as `ambers` starts server
two levels up the amber root directory. This matches the use case
where amber is installed as dependency via npm (so it is present
in `node_modules/amber`.

The new `bin/devserver`, installed by npm as `amber-devsrv`
starts as usual, that is, from amber root.