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

lib/assertion_error.sv

@@ -0,0 +1,5 @@
+// A global error counter, useful for when we're tracking error counts from
+// assertions
+package assertion_error;
+   int errors;
+endpackage : assertion_error

lib/sdvd_defs.sv

@@ -0,0 +1,7 @@
+`ifndef SDVD_DEFS
+`define SDVD_DEFS
+package sdvd_defs;
+    // Playback speed type
+    typedef logic [3:0] SPEED;
+endpackage
+`endif