Rather than hand assemble
https://gist.github.com/sourabhniyogi/5e44600216af117169384a51ab389c8d
we would like to demonstrate how a JAM service written in Rust using
#[polkavm_import(index = 0)]
can be compiled into JAM-ready PVM and include "ecalli {0..22}" calls;  By "JAM-ready" we mean the "0/5/10/15" entry points for is_authorized/refine/accumulate/transfer.

TODO: (1) Get toolchain instructions sufficient to get above Rust compiled into PVM with
 (a) ecalli 16/17/3 in place of import/export (refine) + write (accumulate)
 (b) entrypoints 0/5/10/15 going into is_authorized/refine/accumulate/on_transfer
(2) get polkatool to output .pvm byte code with (1b) streamlined

Sample execution: (after cargo build of jam-service-fib)
./target/release/polkatool jam-service ~/polkavm/guest-programs/jam-service-fib/target/riscv32ema-unknown-none-elf/release/jam-service-fib