Test raw SD read. Works (slow; w/enc 27kB/s, wo/enc 60kB/s).
SD code works on xmega (read 150kB/s).
Code cleanup (serial helpers).
Code cleanup.
Butcher (block r/w only) and move sd_raw code. Fix 512.
Merge branch 'sd' of github.com:flabbergast/enstix into sd