Fixed up debouncer and added some assertions

I moved around where packages are. I couldn't find any evidence of where
other people put them, but for now they are in the `lib/` folder. Other
infrastructure changes are that all the weird includes we need to make
the linter happy are gated behind ifdefs, so they don't mess with
vivado.

I kinda can't believe concurrent assertions work because there's so
little info about them, good to ssee they actually do something

design/audio/audio_buffer.sv

@@ -1,4 +1,6 @@
-`include "sdvd_defs.sv"
+`ifdef VERILATOR
+    `include "sdvd_defs.sv"
+`endif
 import sdvd_defs::SPEED;
 
 //this interfaces with block ram