try and get rid of stepAgain

[kevinbarabash]

Instead just return the location information in the yielded object for function calls and sequence expressions.

[kevinbarabash]

The goal is yield location information about the next expression using the current YieldStatement. Unfortunately, this is not always possible because you don't always know the next expression at compile time, e.g. ternary statements.

Look into replacing all functional calls with thunks that can be called later. This will allow us to yield the location of the expression we're about to call. All function calls will be made outside of the generator.