Feature Request: Reference tracking

[ZeWaka]

Extools had an ability to get forwards and backward references to an object, for debugging hard Dels.

It would be wonderful if auxtools had this same functionality.

[sohpeach]

The issues with this in extools were:

• memory usage, it can't stay in ram (at least in the byond address space)
• detecting deleted lists/datums. The code extools hooked to do this is not always used by byond, as various call sites to it have been inlined by the compiler

Fixing the latter is hard or impossible