Entry point model

[bryancatanzaro]

The compiler currently assumes there is one entry point function, and this entry point is the only one which receives and returns containers. All other non-nested functions are inlined. This is problematic for several reasons:

1. Conditional expressions aren't handled correctly. x if b else y
2. Short circuit binary operations aren't handled correctly if x or y:

We need to change from an "entry point" model in the compiler to a parallelism nesting level, and outermost functions can all receive and return containers.