- Remove NO_VALUE and ExpandedValue::None.
- Remove the Default implelmentation for Value.
- InstructionData::second_result() returns an Option<Value>.
- InstructionData::second_result() returns a reference to the packed
option.
Give these crates each a more standard directory layout with sources in
a 'src' sub-sirectory and Cargo.toml in the top lib/foo directory.
Add license and description fields to each.
The build script for the cretonne crate now lives in
'lib/cretonne/build.rs' separating it from the normal library sources
under 'lib/cretonne/src'.
