General RDDL Improvements & Support

[mejrpete]

As discussed on The Planning Community slack (with Guillem Francès and Emil Keyder). I am interested in extending the existing RDDL support in tarski (and want to do it as much as possible in consultation with the maintainers!). The goal of this issue is to discuss general improvements, identify which are relevant to the core tarski project, and make sure implementations of new features and support are appropriate in design and integration.

Examples include:

• Support for IPPC-2018-style domain and instance files
• Support for using boolean values as 0/1 integers in arithmetic (useful for standard patterns for reward, CPT, and constraint definitions)
• Shared definitions of ConstraintType and Requirements types (defined and used in io.rddl.Writer, but needed in code which uses the Task API).
• Possibly improved/additional Task API support for domain requirements

Simple bug reports and fixes are omitted since I assume those should be submitted as separate issues and submitted fixes in a normal workflow (please correct me if I'm wrong!)

Thanks!