Switch to generated solution files

[jbatte47]

As an architect, I want to generate the files needed by Visual Studio using a simpler set of files with a generator, so that the scope of project- and solution-level changes is reduced dramatically over time.

Expectation:

1. rake will be used to generate relevant files
   1. rake generate
   2. rake vs_open ← depends on generate
   3. rake watch
   4. rake vs_edit ← depends on vs_open, watch
2. .gitignore will be updated to exclude *.csproj / *.sln; projects and solutions are deleted
3. New, minimal file set:
   1. solution.json ← solution / project / dependency metadata
   2. generator.yml ← generator config options