[api] we must be able to override from where assemblies are loaded

[spouliot]

The current code assume they will be with the executable. That's not gonna work for all scenarios, e.g. plugins. PR#42 ran into this issue while adding Xcode-based unit tests. There's a band-aid API to move things forward but it should be revisited to cover more scenarios*

• creating a .framework will also require a different location, c.c. @rolfbjarne

reference: #42

[tritao]

We got APIs for this now in the runtime