v1.7.3

AetherShell v1.7.3

Completes the cross-compilation work. All seven release targets build for the
first time since at least v1.3.1.

aarch64 compiled cleanly once the dependency blockers were gone, then failed to
link: cargo used the host `cc`. The workflow had been installing
gcc-aarch64-linux-gnu all along without anything pointing cargo at it.
.cargo/config.toml now does, and is excluded from the published crate so a
native aarch64 `cargo install` does not demand a cross toolchain.

  1.7.1  openssl-sys  — reqwest default-features pulled native-tls
  1.7.2  alsa-sys     — an unused rodio dependency
  1.7.3  wrong linker — host cc used for a cross target