swmm-toolkit dlls not on Windows path

[michaeltryby]

When importing swmm.toolkit, load of _output module fails because linked library swmm-output.dll can not be found at runtime.

Problem does not occur when package installed under conda.

Traceback (most recent call last):
  File "C:\hostedtoolcache\windows\Python\3.7.7\x64\lib\sitepackages\nrtest_swmm\output_reader.py", line 21, in <module> 
    from swmm.toolkit import output, output_enum
  File "C:\hostedtoolcache\windows\Python\3.7.7\x64\lib\site-packages\swmm\toolkit\output.py", line 13, in <module>
    from . import _output
ImportError: DLL load failed: The specified module could not be found.