cocotb integration

[JulianKemmerer]

https://docs.cocotb.org/en/stable/

Seems pretty powerful and have seen some nice looking examples...

Being in python too makes for integration with existing PipelineC code infrastructure even easier...

[JulianKemmerer]

Basic support is there, see --sim --cocotb --ghdl for example.
Want to support debug wires waiting on #119

For now only tools in the user path are supported since otherwise needs more cocotb specific config/env var setting/etc

[JulianKemmerer]

^also only GHDL is supported right now

[JulianKemmerer]

Supporting template generated sim files for just GHDL --ghdl is enough for now - can follow up for Modelsim templates/specifics as requested/needed...
--sim --cocotb are the general flags

And then any cocotb makefile is also supported
--sim --cocotb --makefile /your/Makefile

Template python code can evolve as needed - for now allows basic read and write variable = function call looking generated code - can get fancy later