Multi Project Harness

• This is a proposal for handling multiple projects in the user project area of the Caravel harness
• This is a fork of caravel with https://github.com/mattvenn/multi-project-harness added to /verilog/rtl/
• user_project_wrapper is then adjusted to instantiate https://github.com/mattvenn/multi-project-harness/blob/main/multi_project_harness.v