Improve the clarity in the instruction documentation about opcodes

The document emphasizes the word ‘directly’ to stress that LNVL does
not directly create instructions from content, instead creating
opcodes first that later become instructions.  But the actual markup
of the document does not drive home this point that clearly.  The
important part to emphasize is that LNVL creates opcodes first, then
instructions, and so the markup should reflect that emphasis.
Fix a typo in the instruction documentation over drawCurrentContent()

The document incorrectly refers to a non-existent function instead of
the actual Scene:drawCurrentContent() method.
Correctly document the ‘name’ argument of the ‘change-scene’ opcode

The documentation says that ‘change-scene’ accepts no arguments but
that is incorrect.  It requires the name of a scene to change to.
Remove unused methods from the ‘04’ example script

We do not need to use ‘says’ with characters anymore, and we have
since renamed jumpTo() to Scene.changeTo().  The logic for menus is
still not finished though, so we leave those parts as they are.