Automatically include tests in reference test project.
Added Reference tests to build and project file.

The reference tests are now automatically built (on Windows) to prevent
accidental build errors in that project (as introduced in #204).

A RefTest target has been added to run the reference tests.

Minor restructuring of the project file.
Updated CONTRIBUTING since things are a bit easier now.
Merge pull request #216 from ygra/reference-tests

Some build system improvements to reference tests