Create test directory; restore test10 & demos 2-3; add Conda install file & instructions

[aufdenkampe]

@rheaphy & @PaulDudaRESPEC, here's our first pull request. I'm making it to your master branch because this includes a restoration of some valuable test & demo files, related documentation, and our installation files & instructions.

We'll be pulling these changes into our development branch to keep that up to date as we start working on the water quality modules.

cc: @steveskrip, @ptomasula, @benjamincrary

[aufdenkampe]

@rheaphy, thanks!

Our plan is to start adding testing models, storing each HSPF test case in our repo:

• in tests/XXmodel/
  • store UCI, WMD and other input files
  • Git-track any changes to UCI that we make to get the model to run in HSP2
  • Store HSP2 model outputs & testing files
• In tests/XXmodel/HSPFresults/ store all HSPF output files,
  • in each of these formats: HSPF native formats, LimnoTech’s WinModel Excel file, Pandas output binary from reading Excel file
  • These files will be considered static
  • Are there other output file formats we might consider?