Random access memory

[bobbinth]

This PR will attempt to add support for random access memory. This requires:

• Move PUSH operation out of high-degree operation class into its own class.
• Add MEMRR operation to high-degree operation class.
• Add memory state register.
• Add MLOAD and MSTORE machine instructions to low-degree instruction class.
• Define load and store assembly instructions.
• Update external interfaces.
• Update documentation.