* src: directly serialize Function metadata as func.yaml
Functions now save directly to func.yaml using .Write().
Fixes a serialization error where defaults were not respected on load.
Moves runtime and template defaults into function constructor.
Extracts Function validation (was config validation) into separate functions.
Extracts associated test files (validation) into separate unit test files.
Updates schema generator to use Function
* comment spelling and re-enabling tests
David Simansky
Luke Kingland