Unfortunately:

1. Read can read bytes and return an EOF at the same time (could cause us to
fail to parse something that's actually correct).
2. ReadByte is not allowed to do this (fixed in PeekByte).
3. Returning EOF on _actual_ error cases can cause the error to be silently
dropped somewhere up the stack (where the EOF may be interpreted as "I'm done").
I've replaced EOF with ErrUnexpectedEOF where appropriate.

This crap really shouldn't be necessary, but such is life.