iASL: Allow 0-length packages for variable-length packages.

For the predefined names that return fully variable-length packages,
allow a zero-length package with no warning, since it is
technically a legal construct (and BIOS writers use it.)
Disassembler: Add warnings for unresolved control methods.

Flags the case where external control methods are unresolved,
meaning that the disassembler had no idea how many arguments
to parse for the method invocation.
Update .gitignore

Add additional script.