Add tcl inputs.

[stridge-cruxml]

Add tcl inputs to rules_vivado. It is common to require custom tcl between the various stages, to run reports or an additional optimization stage, examine resources etc.

Additionally, this allows the inclusion of bd. To do this:

In vivado GUI, export the board design to a tcl file. Add this line to the bottom of that tcl file:

generate_target all [get_files *${design_name}.bd]

Then add the tcl to pre_synth_tcl in vivado_bitstream. You will also need to generate the wrapper and set that as the top module though.

[stridge-cruxml]

Just realized I committed a bunch of auto formatting changes (with black). Happy to revert if you prefer.

[agoessling]

Thanks for this as well. Maybe an unpopular opinion, but I use single quotes and two space indent for my python styled after Google's internal code. I really should add a .pylintrc. Could you please revert the formatting changes and I'll review? It's currently hard to separate formatting from true changes.

Also before merge, could you add an example of including a simple tcl file in examples?