Organise project into folders

* "lib" folder
* clone repo, copy Rhino/Gh references and build!
* room for more folders (docs, scripts, tools, etc.)
Merge remote-tracking branch 'upstream/master' into folders
Rename test project (Plankton.Test -> PlanktonTests)
Single build directory (with xml documentation)

* see src/bin/{Release,Debug}/
* xml documentation only generated in Release mode
Merge pull request #7 from pearswj/folders

Folders