User can now provide a Function or an ApplicationInitializer. Also
the initializer can create a FunctionRegistration with the handler
name instead of a bean with the handler name. Better control of
input and output types that way.
Fixes gh-231
Some tests still ignored.
Also adds draft functional bean registration support. The AWS sample
is using that now (it starts up 4x faster in AWS). To activate the
functional beans user has to supply a main class of type
ApplicationContextInitializer.
Instead of an app, it is now a library with some utilities
(principally ApplicationBootstrap) for launching a Spring Boot
application, extracting a function, and registering it in the
FunctionRegistry.
