Sync from Tumbleweed

[ams]

This syncs the repo against any changes at Tumbleweed, incorporating the following changes:

• Top level projects have been renamed (A7 -> arty_a7).
• The memory_controller_A7 is now ram_controller_arty_a7 (and the old one is removed).
• Chaosnet support which was very much incomplete has been removed.
• Pipistrello related files have been restored in favour of what is on Tumbleweed since the current one don't work.
• Updated with changes from Tumbleweed synchronizing all common files (mainly Verilog-2001).
• The Vivado project has been updated accordingly.

[ams]

I think this is ready. I've vomited the runs between this PR and your tree and they look very much the same.