fix numerous warnings

[m4b]

Please review:

There are two warnings left; I don't know how to fix them, they seem spurious to me.

1. adds unwraps to mos/avr semantics
2. removes unused imports
3. removes unused mutations
4. adds some minor docs
5. adds allow empty docs to abstractinterp because i don't know how to doc it
6. other misc changes

I don't want to do this again; we need to make buildbox fail on warnings after above two warnings fixed.

Also if you want to change something, please just update the PR with the commits that change it how you want; e.g., I suspect the unwraps are undesirable, but this would require larger refactor of changing function type and I didn't feel like messing with it cause I don't know that code

[flanfly]

Thanks! Don't worry about the unwraps. If mnemonic or jump fails it's a fatal error anyway.

[coveralls]

Coverage increased (+0.1%) to 61.017% when pulling 6782965075a8313bd7e52661723f7595d5d0ecc4 on m4b:fix_warnings into bbf38817924a5c061c6bd659d44ea6250e3903be on das-labor:master.

[coveralls]

Coverage increased (+0.2%) to 61.069% when pulling 50f918f9f0494e1a14565644579ad01d699046b9 on m4b:fix_warnings into bbf38817924a5c061c6bd659d44ea6250e3903be on das-labor:master.

[coveralls]

Coverage decreased (-0.07%) to 60.843% when pulling a8651729cf9d0d120e13df0ee8be43de1996226c on m4b:fix_warnings into bbf38817924a5c061c6bd659d44ea6250e3903be on das-labor:master.

[coveralls]

Coverage increased (+0.02%) to 60.93% when pulling 470fc0d61a2305129aadfc3f73cf04a567fc875f on m4b:fix_warnings into bbf38817924a5c061c6bd659d44ea6250e3903be on das-labor:master.

[coveralls]

Coverage decreased (-0.03%) to 60.878% when pulling 7862fe606a80ef548f1d37e26f0b7e6779a8bfa7 on m4b:fix_warnings into bbf38817924a5c061c6bd659d44ea6250e3903be on das-labor:master.

[coveralls]

Coverage decreased (-0.05%) to 60.86% when pulling 7862fe606a80ef548f1d37e26f0b7e6779a8bfa7 on m4b:fix_warnings into bbf38817924a5c061c6bd659d44ea6250e3903be on das-labor:master.