Reference library path searching feature

**Is your feature request related to a problem? Please describe.**
When reverse engineering a third-party project, its libraries(dlls) are scattered in different directories. 
It's very painful to drag every dll into ILSpy.

**Describe the solution you'd like**
Can you add a feature to edit dll search path, and append custom dll search paths?
just like `LD_LIBRARY_PATH` or `PATH`.

