to its actual behaviour: That it uses the least amount of bytes unless
overridden.

The current documentation leaves it undefined how many bytes will be used
when no number to use has been given explicitly. But several estimates
(used to write EBML Master elements with a small length field) require
this number to be the least amount of bytes to work. Therefore change
the documentation; and remove a comment about writing length fields
indicating "unkown length". It has been outdated since 0580a122.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>