Code clean-up around "git serve".
* ab/serve-cleanup:
upload-pack: document and rename --advertise-refs
serve.[ch]: remove "serve_options", split up --advertise-refs code
{upload,receive}-pack tests: add --advertise-refs tests
serve.c: move version line to advertise_capabilities()
serve: move transfer.advertiseSID check into session_id_advertise()
serve.[ch]: don't pass "struct strvec *keys" to commands
serve: use designated initializers
transport: use designated initializers
transport: rename "fetch" in transport_vtable to "fetch_refs"
serve: mark has_capability() as static
5331af2352