examples: make builds in examples dependent on ddpg (for testing)

Signed-off-by: Peter Williams <pwil3058@gmail.com>
symbols: make Symbol components known at creation time constants

Signed-off-by: Peter Williams <pwil3058@gmail.com>
symbols: remove allSymbols member from SymbolTable for simplification

Signed-off-by: Peter Williams <pwil3058@gmail.com>
symbols: add invariant to SymbolTable (prelude changing to struct)

Signed-off-by: Peter Williams <pwil3058@gmail.com>