Make ashuffle release binaries fully static

[joshkunz]

(except for libc)

In #142, the user's system was running an old version of libmdclient that did not support oneshot single mode leading to some confusing behavior. We should probably build the release binaries with a static libmpdclient for consistency (preserving the non-static builds for distros).

I also checked and it appears that libmpdclient has a compatible license (BSDv2).