* cannon: Increment MIPS.sol version

* cannon: Add syscall args helper

* cannon: Extract mmap helper

* cannon: Extract sysRead helper

Also:
- Extract solidity memory helpers into new lib.
- Reorganize syscall constants.

* cannon: Add NatSpec documentation to solidity syscall helpers

* cannon: Extract sysWrite helper

* cannon: Use consistent naming convention

* cannon: Extract sysFcntl helper, fix typos

* cannon: Consolidate comments, fix formatting

* cannon: Add helper for setting registers, pc fields

* cannon: Reorganize syscall constants

* cannon: Fix MIPSMemory import

* cannon: Run semver-lock and snapshots

* cannon: Explicitly inject proof offsets into helper fns

Proofs offsets may differ between implementations, so these values must
be passed into helper functions rather than calculated internally.

* cannon: Remove hard-coded state.memRoot references from MIPSMemory.sol

* cannon: Work around stack too deep error

* cannon: Rework stack-too-deep fix

* cannon: Run semver-lock and snapshots

* cannon: Validate calldata size directly in readMem, writeMem

* cannon: Run semver-lock and snapshots