Add bitwise operations

[effectfully]

All of them.

I assume we want to use the ones' complement representation, but I'll check this just to be sure.

[effectfully]

gosh it's a rabbit hole... So little-endian is "the least significant bit goes first", but that "first" can arbitrarily mean either "leftmost" or "rightmost" (both orderings are used).

So I'll just use the most common representation: "the least significant bit is the rightmost one" without talking about endianess.

I'll also use two's complement, because it also seems to be the most common thing

[effectfully]

It actually makes sense to have another type of variables: unpacked field elements (i.e. ones in binary form). This is because we do not want to unpack elements, perform an operation and pack everything back downstream, because we will want to perform several bitwise operations in a row.