parser: update the state machine README and fix an off by 1 padding error

Update the state machine readme to better reflect how the chfa is encoded and works. It still needs a lot more but fixes several errors in the doc and adds some info about state differential encoding, oobs, and comb compression.

In addition fix an off by own error during chfa encoding. This has likely never triggered as it gets hidden by being in a section that is being in a section that is padded to an 8 byte boundary.

Signed-off-by: John Johansen john.johansen@canonical.com