Handle passing literal values to compiler

[seibert]

There are some unused parameters in the compiler APIs to pass literal values (i.e. values that should be frozen at compile time and can be used to influence code generation) to the compiler. These eventually need to be wired up after #173, which will make the distinction between compile-time literal values (which won't be wrapped in a placeholder class) and runtime values (which will be wrapped in placeholder classes) more clear.

(Eventually we will need some additional logic to allow things like a trained graph embedding to be treated as a literal so it can be fused with another ML algorithms.)