Added modules to read sdcard data and cmd response

These were realy headaches but the testbenches are passing. We need to
take a look at the audio_buffer testbench for sure, it is way wrong and
needs reworked to use the interface. Should do a pass through every
module probably.

doc/bugs.md

@@ -30,3 +30,12 @@
 ### command_sender
 - output ready signal was delay a cycle because it was set by sequential logic,
   detected in testing, changed it to a combinational output for 1 cycle speedup
+
+### read_command
+- response_type was not getting correctly stored/set, breaking the module
+  entirely. Detected in testbench
+- off-by-one error detected in the counter
+
+## read_data
+- audio buffer address to write to was never changing, caught in simulation
+- some off-by-one errors in the byte shifting were found and corrected