Adds smed, an assembler and linker written in c0 that takes GNU as and ld
off the path from c0 source to a running program, and verify_bootstrap.sh,
a trusting-trust audit with diverse double compiling against a second C
compiler. gcc is no longer required, tcc bootstraps an identical compiler
and is reachable from a hand-auditable seed. TRUST.md documents what is
trusted, what is checked, and what none of it proves.