Support a second parser (other than Surelog) #319

The goal of UHDM is to allow "users" (like Yosys, Verilator and Icarus) of a SystemVerilog parsers not to care about the exact parser implementation. However, currently the only parser which exposes the UHDM interface is Surelog.

Adding a second parser which also exposed the UHDM API would help verify that the API isn't over fitted to Surelog in any way.