Version 0.7.0

There have been many changes since the last release, focused on performance and features. These changes caused a number of API changes and behavioural changes, the most significant of which are listed below.

• Requires all Starlark types support Serialize, and provide derive(NoSerialize) to easily add a failing Serialize.
• Remove collection_json.
• Support the latest gazebo dependency.
• SmallSet now returns an ExactSizeIterator.
• Many optimisations, particularly around strings.
• Many optimisations to the bytecode compiler.
• Rename functions for working with constant strings.
• Add StringValue type, for Values which are known to be strings.
• Remove SimpleValue.
• Remove the Span type.
• Rename SmallHashResult to SmallHashValue.
• Improve error messages on the wrong number of positional arguments.
• Remove some float-related functions from the API.
• Adjust the profiling API to make it more modular.
• Add support for validators when freezing.