[WIP] Scans

• Closes #46 (closed)
• Closes #32 (closed)
• Closes #51 (closed)

Work in progress closing:

• #42
• #40 (closed)

Partially addressed, but not intended to close:

• #34

Still needs:

• Precompute support for tuple-typed substitution rules (req'd for two level segmented scan)
• Address todos, fixmes in the code
• Finish writing scan tests
• Finish writing tests for all auxiliary functions added (e.g. add_nosync_to_instructions)
• Come up with a consistent naming convention for auto-generated scan code