Add haddocks to new `compile`/`TracingMode` API

[peter-mlabs]

TracingMode doesn't have any haddocks, and its not immediately apparent what DetTracing does.

[L-as]

deterministic tracing

[peter-mlabs]

What does deterministic tracing do vs regular tracing?

[L-as]

@peter-mlabs When you're doing tests, you often want the compiled code not to change if the source code hasn't. Without DetTracing, moving around lines (without changing anything), will change the trace messages, since they will include the line numbers.

[peter-mlabs]

Ah good! Thanks