Testing - Check build dependencies and sequence for OutOfProcess tests

From @eeaston:

> Another gotchya I think I’m seeing is that when running the test using out of process mode, I need to do a project->build in visual studio, instead of just running the test and expecting it to do the build for me. If I don’t do this, then it uses the previous built binaries.

If this is tricky to fix we should at least document it in the [Readme](https://github.com/Excel-DNA/DeveloperTools/blob/master/ExcelDna.Testing/Readme.md).

Start by reading the OutOfProcess test setup and the ExcelDna.Testing/Readme.md. Reproduce the issue by running an OutOfProcess test without a Visual Studio project-build, then compare the result after building the project. Done means the tests use current binaries automatically, or the required build sequence is clearly documented in the Readme.

Written by the indexing model from the issue text.