Dictionary

A dictionary entry has this structure:

- Xb name. Arbitrary long number of character (but can't be
  bigger than input buffer, of course). not null-terminated
- 2b prev offset
- 1b size + IMMEDIATE flag
- 1b code pointer (always jumps in the <0x100 range)
- Parameter field (PF)

The prev offset is the number of bytes between the prev field
and the previous word's code pointer.

The size + flag indicate the size of the name field, with the
7th bit being the IMMEDIATE flag.                       (cont.)