WIP: Alpine docker image

I've been trying to create a lighter weight docker image by compiling with musl to create a single static binary alpine image. This really isn't that important since the ubuntu image is only like 35MB, but it's bugging me that I can't get it working, and I thought it would be pretty cool.

The current error is basically identical to https://github.com/rust-lang/rust/issues/36710

note: /usr/lib/gcc/x86_64-alpine-linux-musl/9.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: /usr/local/lib/libvrpn.a(vrpn_Thread.C.o): undefined reference to symbol 'pthread_kill'
         /usr/lib/gcc/x86_64-alpine-linux-musl/9.3.0/../../../../x86_64-alpine-linux-musl/bin/ld: /lib/libc.musl-x86_64.so.1: error adding symbols: DSO missing from command line
         collect2: error: ld returned 1 exit status

Also related:

• https://github.com/emk/rust-musl-builder/issues/65
• https://github.com/messense/rust-musl-cross
• https://github.com/rust-embedded/cross
• https://github.com/vrpn/vrpn/issues/256

And reasons not to do this:

• https://andygrove.io/2020/05/why-musl-extremely-slow/