Implement element-addressable memory

[plafer]

Closes #1064

Note that I changed the batch column to hold 4 * previous_defn_of_batch (now effectively the first address in the batch). This is to avoid a needless division per row in the processor.

This PR does not address the concern raised #1064 (comment); we should do that one in a subsequent PR, as it is a backend thing, and getting this PR out the door will allow miden-base and the compiler to start working fixing their code.

Left to do:

• document the hashing behavior of pipe_double_words_to_memory and pipe_words_to_memory
• docs
  • Make sure to document that procedure locals in MASM are words
• address all TODO(plafer)s

[plafer]

@bobbinth I am done implementing the processor part of the change, which is ready for review. All tests in the processor pass (except 2 which run the verifier, or verify the correctness of the bus).

Left to do after (high-level):

• fix bus
• update air constraints
• update the book
• a bit of cleanup (the TODO(plafer)'s)