Function design & related issues

[Ryan Nett]

A little late, but I've written up initial design docs for functions.  This ended up requiring changes to initialization and variable handling (which is why it took so long).

Initialization and variables: https://github.com/tensorflow/java/issues/237

Functions: https://github.com/tensorflow/java/issues/238

Questions and comments are welcome, I expect we'll talk about them at the next core meeting too.